FORTIFICATION

Is the art of securing a portion of ground, whether occupied by a town, or including within it a dock-yard, port, or harbour, or serving, in military language, as the position of an army, from the attack of an enemy, by surrounding or covering it with works of defence; and as such works are so many obstacles placed in the way of the advance of their assailants, whilst they are at the same time the means of sheltering the defenders, it is the art of enabling a small number of men to defend themselves against the attack of a much larger. Various modifying terms have been adopted in connection with the general one of fortification, but none of them are of much use in considering this subject, and some may lead to error, by inducing an engineer to restrict himself under some circumstances to a very limited view of his subject. Thus, fortification natural and fortification artificial, imply a very useless distinction, as every engineer must avail himself both of the natural advantages or obstacles of the ground, as well as of the obstacles his science and genius enable him to add to them; and thus in every fortification nature and art must act together. Again, fortification regular and fortification irregular, are terms equally defective, as no fortification can be possibly regular unless it should so happen that the ground it occupies, as well as the ground surrounding it, is on all sides perfectly identical in its levels and general character. Fortification permanent and fortification field or temporary, refer again only to the immediate object of the works, or to the application of the science, and in no way affect its principles, which remain the same whether the work is a simple earthen intrenchment, or a great fortress surrounded by masonry walls. Fortification offensive and fortification defensive, are of all the most objectionable terms, since, strange as it may appear, they imply a contradiction to fact, as the perfection of defence depends as much on its active or offensive operations as on the protection its covering works afford, whilst the perfection of attack is equally dependent on the skill with which its covering works are constructed and pushed forward towards the fortress attacked, as on its offensive operations, or on the fire of its batteries.

The principles of defence then should be studied unshackled by any of these limiting distinctions, and the engineer should apply his means to his end, using without restriction the works best suited to his purpose; and it is in this way that the study of the subject will be here treated.

ELEMENTARY FORTIFICATION.

It is often desirable to examine the exact meaning of technical words, as a ready mode of acquiring a distinct notion of the ideas they were intended to convey; and of obtaining a glimpse of the historical progress of the science in which they are used. Fortify, Fortification, Fortress, Fort, are all words depending on the Latin words fortis, forte, strong, and fortifico or forte facio, to make strong; hence the idea they suggest is that, by some artificial or other arrangement, additional strength is bestowed upon one combatant over another, or upon one party of combatants over another party. A shield, the trunk of a tree, or bank of earth, or any other similar contrivance which shelters the body of one soldier from the missiles of his opponent whilst it leaves him free to discharge his own, may be considered a simple element of fortification.

A bank of earth, when reduced to the requisite thickness, and moulded into a proper form, with such slopes as the particular tenacity of the earth may require to insure stability, or which the intended direction of the fire over its summit may render necessary, becomes a parapet, so

called from the Italian words para, a defence or guard, and petto, the breast, or, in English, a breastwork. If the breastwork or parapet were only made sufficiently high to permit the soldier to fire over it, he would be greatly exposed after firing, and be forced to crouch down in order to obtain cover. The parapet is therefore made sufficiently high to cover the soldier when standing up, so as to enable him with ease and security to reload, as well as to move from one place to another. This increased height has rendered it necessary to introduce a banquette or step (accessible by an easy slope) from which the soldier can fire and then retire by the interior slope to the lower ground behind it; the name banquette being derived from banchetta, a little bench or step. As parapets are usually formed artificially, the earth for their construction is derived from a ditch, which being dug immediately in front of and parallel to the parapet, forms by its depth an additional obstruction to an advancing enemy. Ordinary intrenchments are formed of the simple parapet and ditch, but in forts and fortresses the height is still further augmented by elevating the parapet on another mound of earth called the rampart (riparo, in Italian), and as this additional mass requires a greater quantity of earth, the ditch is also made both wider and deeper. In this manner the difficulties of attack are increased, additional cover is given to the magazines or other buildings within the fortress, and the command over the country is increased and improved in efficiency, by elevating the soldier so that he can see over the many minor obstacles likely to restrict his field of view. A natural and simple mode of distinction may be therefore derived from the presence or absence of a rampart, and the two leading sections of the subject stated thus: parapet, or field fortification, and rampart, or town fortification.

In order to study efficiently the results of combining together these simple elements, and forming from them extensive works of defence, it is necessary that we should know the manner in which such works are represented on paper. As in architecture, of which in earlier times fortification was only a military branch, this is effected by the plan, the section, and the elevation, of which the two first are the most important. The plan of a work is the orthographic projection of the lines of intersection of the planes of its slopes on the plane of construction. The elevation is a similar projection on a vertical plane. The section or

Fig. 1.

profile is taken on a plane perpendicular to the lines of intersection of the planes or slopes, and therefore represents

the traces of these planes on the sectional plane. Fig. 1 represents a small portion of a simple parapet in plan and profile, and leads to the following explanation of terms:—

In the plan, cc represents the crest of the parapet or highest ridge line of the work. In delineating the mere outline form of a work, it is this line which is always drawn, and is called the trace. Between cc and ee is the superior slope; between ee and a line parallel to it, through s of the profile, is the exterior slope, prolonged in this case to the bottom of the ditch dd, being continuous with the scarp sd; gg, crest of the glacis, or ridge of a slightly elevated mound of earth raised on the exterior edge of the ditch, or of the counterscarp, and sloping gently outward, so as to bring the assailants directly in the prolongation of the superior slope of the parapet, and therefore into the line of fire from its crest, and by its elevation to increase the amount of descent into the ditch. Within the crest of the parapet is seen the interior slope of the parapet, bounded by bb, the banquette, between bb and bb, and the interior slope of the banquette, bounded by aa.

Relief.—This term is adopted to show either the height of any point of the work above the plane of construction,

which is sometimes equivalent to the plane of sight, and may then be called constructive relief; or the height above the bottom of the ditch, when it may be called absolute relief. The relief taken in the latter sense is a very important datum, as it expresses the total amount of the obstruction offered by the parapet and ditch to the ascent of the assailant, and also as it is necessary in regulating the length of lines, which mutually defend each other, as will be seen hereafter. Relief of a work refers to the relief of the crest of its parapet. Command of a work means the height of the crest of its parapet, either above the plane of sight if horizontal, or above any point of that plane specially referred to, or above the crest of the parapet of any other work in front of it; the difference of height, therefore, between the crest of the parapet in fig. 1 over the crest of the glacis is the command of the parapet over the glacis; in the one case it is absolute, in the other relative command. An examination of the profile figure brings also under consideration, in respect to the row of palisades, another simple principle, namely, that an enemy should be stopped as he advances to the parapet by every obstacle which can be thrown in his way, and thus kept exposed as long as possible to the fire either of the

Fig. 2.

work in front of him, or of some other work taking him in flank; if simply opposed by a front fire from the parapet, palisades, arranged as these are, would only check for a very short time the progress of an enemy, and are more useful for gaining time on the part of the defenders than for ultimate defence.

Obstacles against approaches. Many other obstacles may, however, be so arranged as to assist materially in rendering even the simple direct fire more effective.

Abattis.—These are formed of trees cut down, and arranged side by side with the branches interlaced together outwards, and the stems inwards; the branches should be freed from foliage, and their ends cut sharp. They may

depends on direct fire alone; and in these cases an arrangement of the profile, as here figured with obstacles, would be far more effective in checking an enemy than an ordinary profile though in itself more difficult of ascent, without such obstacles, and in consequence would render it impossible that an ordinarily watchful garrison should be surprised; and this is a very important consideration, as a vigorous and bold enemy could scarcely be stopped if he had succeeded in arriving at the foot of the scarp unchecked.

Fig. 3 is another adaptation of an abattis formed only of large branches securely picketed down to the ground. In this case the form of the ground is taken advantage of, and even the profile of the defensive line is modified, a trench being cut out behind it, and the banquette being formed on the surface of the ground itself. The engineer will often, by simple arrangements of this kind, be able to carry his defensive lines over a large extent of ground in a short period of time, and to obtain a much more effective defence from the natural facilities afforded by the ground than he would have done by superadding to them, at the expense of great labour and much time, elevated works, not so well fitted to scour the face of the ground, and to act immediately upon the obstacles then checking the progress of the assailants.

Chevaux-de-frise.—The cheval-de-frise is an artificial substitute for an abattis. It consists of a strong horizontal beam, about 12 feet long and 9 inches square, through which

be arranged either in one or more rows, and when placed so that the fire from the parapet should sweep along their summits, they would, their stems being firmly fastened down by pickets to the ground and partly buried in it, occasion great loss to the enemy whilst attempting to remove them under fire.

Fig. 2 exhibits an arrangement of this kind; and it will be observed that on this profile the exterior slope of the parapet and the scarp have been formed into one gentle slope, whilst the counterscarp retains its ordinary slope. By this modification the difficulty of descending into the ditch remains as before, and the sloping pickets in front of the abattis prevents the assailants from immediately endeavouring to clear it away. In simple inclosed works, such as redoubts, as well as in lines, the defence frequently

are passed strong lance-like rods of either wood or iron, sharp at both ends, and about 6 inches apart. Several of these

Fig. 3.

Fig. 4.

Fortification. may be joined together by means of a ring at one end and the hook at the other end of the beam. The difficulty of making chevaux-de-frise, as their construction requires a number of carpenters and much wood, renders them unfitted for sudden emergencies, and they are also, under ordinary circumstances, easily removed or destroyed; but with these, as with all military implements, there may be opportunities of using them with effect. If planted at the bottom of a hol-

low, exposed to a well-directed fire, and so placed that they must either be pushed uphill forward or pulled uphill backward, and then secured to the ground, either by chains, or by being fastened to upright posts, they would often prove a formidable obstacle. They are more generally used as a barrier to close an open work.

Fraises.—The fraise is distinguished from the palisade by being fixed in a horizontal, or nearly a horizontal position.

Fig. 5.

They are made about 10 feet long and 5 inches thick, being bound together by two ties, one nailed above and the other below them; without which precaution they would be much more easily torn away. They are sometimes fixed on the counterscarp as well as on the scarp.

Fig. 5 represents, in section, a row of fraises on the scarp. In this profile the ordinary banquette for musketry is represented by dotted lines below a wider terreplein formed for artillery to fire over the parapet, or a barbette, as it is usually called; but this will be more fully explained in a future paragraph.

Chausse-trapes.—These are made of four points of iron so arranged that one should always project upward in whatever manner they may be thrown on the ground. The points are either 2 or 4 inches long, and they are soen over a space about 12 feet broad. Without doubt, troops coming suddenly, and in the dark, on such obstacles as these, would be much annoyed by them; and, in consequence, they were formerly much used, more so than they are now.

Trous-de-loup, or wolf-traps, are holes made in the ground in the form of a truncated cone, the sides of which are as little sloped as is consistent with the stability of the soil. They are made from 5 to 6 feet deep, and 6 or 8 feet in diameter. At the bottom a sharp picket is fixed, from 3 to 4 feet long, or, in place of it, the branch of a tree cut into sharp points, or a number of smaller sharp pickets, or a quantity of chausse-trapes. The figure shows the arrangement of trous-de-loup proposed by Wénzel, in plan and in section. If along the defensive line of a position, either on the glacis or on the scarp, when gradually sloped as in fig. 2, small trees or shrubs are planted, and on an emergency cut down, and the points of their stumps sharpened, they become very annoying to an assailant. Harrows have also been used, and, in short, every expedient which ingenuity can suggest should be adopted by an engineer to check the progress of an advancing enemy, and to keep him as long as possible under fire.

Stockades.—Before proceeding to an investigation of the principles which should regulate the relief and thickness of ordinary parapets, viewed in reference to simple defensive lines and to direct fire, it is right to notice the stockade as a substitute, and in some circumstances an advantageous one,

for a parapet. The stockade is formed of either one row of stout palisades, or two rows, one behind the other; and the following is one of the simplest modes of constructing it:—

A row of very strong palisades, pointed at the top, from 8 to 12 inches square, is formed, with intervals of 3 inches between every two palisades, and behind this row is formed another corresponding to the open intervals in the first. These second palisades are only from 5 to 7 inches thick, and are cut square at the top, every second one being cut short, or to the length of 4½ inches, so as to fire over it as through a loophole. This stockade is shown in plan, elevation, and section; it has a banquette of earth, which may be replaced when desirable by a wooden step. By cutting out the triangular portion shown in the section, and throwing the earth up against the front of the palisades, an exterior slope and scarp are formed which keeps an enemy constantly in view. Such a stockade as this brought up close to the edge of a steep bank, requiring defence, has a great advantage over a parapet, as the men behind it have a much more effective command of the ground before them when firing through the loopholes than they could possibly have when firing over a parapet. It is here supposed that artillery fire cannot be brought to act in front against the stockade, but it may possibly be brought to act against it in a longitudinal, or, as it is called, enfilade direction; and in this case the line of stockades should be interrupted by traverses, which are usually banks of earth placed transversely to the line they are intended to protect from enfilade fire.

Fig. 6.

Fig. 7.

Fig. 8.

Fig. 9 shows the adaptation of a stockade of this description to the defence of precipitous ground. When stockades

are formed into enclosed works, they constitute what are called "tambours."

It may in a similar manner be desirable to throw an ordinary parapet forward to the edge of a bank, the slope of which supplies the function of a scarp, and hence to dig the ditch behind instead of before it, as in fig. 10, where it will be also observed that the slope of the banquette is broken into two steps, the tenacity of the earth when first excavated allowing it to stand firm; and the principle of this excavated form of structure is also adopted in sunken batteries.

Fig. 9.

Fig. 10.

Sometimes the object of the parapet is merely cover and not active defence, in which case the banquette is omitted as in

Fig. 11.

fig. 11; and the work is called an epauletment. In this profile it will be observed that a space is left between the face of the epauletment and the internal ditch, which is called a berm. Such a space should always be left, whether the ditch is within or without, when the work is to be formed of any considerable elevation, as it forms a stage upon which the builders can stand, and lessens the height to which the diggers have to throw the earth from the ditch; and it is very important to keep the berm clear by throwing forward or back the earth as quickly as it is raised. The distinguish-

Fig. 12.

ing characteristic of an able engineer is to be found in the power of varying his appliances at will;—thus the abattis may become the fraise, or may displace the palisade, as in fig. 12. Were this principle not kept in view, more evil than good would sometimes result from systematic instruction; as the person who had acquired a knowledge of some one

Fig. 13.

contrivance might be found crippled by his constant efforts rather to conform to it than to look about him for some

other better fitted for the existing circumstances. In this profile a berm is represented, as it would be difficult to arrange the abattis, and to build the parapets without it.

The arrangement of the trous-de-loup, combined with stakes driven into the ground, is shown in fig. 13, an advanced glacis having been formed of the earth thrown out of the excavations. The ditch is in this case triangular; and it is scarcely necessary to add that the choice of any particular form must be determined by the engineer from a knowledge of the nature of the ground itself, only remembering that the contents of the ditch, or ditches, must supply material for forming the parapet; and further, that as its depth adds to the difficulty of assault, it should not be diminished except from necessity. After these elementary remarks, the student may be considered prepared to enter on the consideration generally of parapet or field fortification.

RULES FOR DETERMINING THE DIMENSIONS OF PARAPETS.

Determination of the Relief of a Parapet.—First, in respect to the protection of troops in a normal position, where the ground is considered horizontal. Now, the minimum for a simple parapet may be here stated at 6' 6" as a musket ball would penetrate the parapet for about 6' below its crest, and the maximum at 8 feet, a height which gives the defenders perfect security under almost every circumstance of fire, including even that of mounted soldiers.

Defilade.—Secondly, where the ground is uneven, and it is necessary to defilade the work from the point or points which command it. Now, figure 14, No. 1, explains the first case in which the points A, B, C, are on the same level, the distance AB being the space intended to be protected by the parapet at C. The line CF represents the supposed height at which it is presumed the assailants may fire, or in this case 8 ft.; BE will be the same; and AD cut by the line drawn from F to E will also be 8 ft. In fig. 14, No. 2, A, B are still considered to be in one horizontal plane, but C is considerably elevated; and hence, adopting the same data as to height, and drawing the line FE and the line CB parallel to it, AD, or the height of the parapet, equal to AI + ID; ID being equal to BE, or CF, or N, the normal height. Calling also AB, or the distance to be covered, d; AH, or the distance from the commanding point, D; HC, or the height of C above A and B; we have AI : CH :: AB : BH; or AI : H :: d : d + D; and hence

AI = \frac{d}{d + D} \cdot H, \text{ and } AD = N + \frac{d}{d + D} \cdot H \quad (1).

So that the necessary height of the parapet increases as the height of the commanding point increases, or as the distance AB to be defiladed increases; and diminishes as the distance from the commanding point increases. Taking

D = 600 ft., d = 30 ft., H = 60 ft., $AI = \frac{60}{21}$ , or 2 ft. 10 in., and AD, or the height of the crest of the parapet, equal to 8 ft. + 2 ft. 10 in. = 10 ft. 10 in.; or taking D = 1200 ft., or 400 yards, AD = 9' 6".

Fig. 14, No. 3, represents A lower than B by a quantity = AO = GH = h; hence AD = AO + OI + ID, and $OI = \frac{OB \cdot CG}{BG} = \frac{d}{D + d} (H - h)$ , or AD = N + h + $\frac{d}{D + d} (H - h)$ . . . . . (2);

an equation which shows that the deeper A is sunk below B and C, the more elevated must be the parapet, and hence that this is a very unfavourable condition of parapet. For example, let A be 2 ft. below B, and all other data the same, $\frac{d}{D + d} (H - h) = 2 \text{ ft. } 9 \text{ in.}$ , and AD = 8 ft. + 2 ft. 9 in. + 2 ft. = 12 ft. 9 in.; or when D = 1200 ft.,

Fortification. 11 ft. 4 in.; and if it should be necessary to defilade a distance of 90 ft. instead of 30, the heights of the parapet would necessarily become 18 ft. 8 in., and 14 ft. 2 in.

Figure 14: Four diagrams (No. 1, No. 2, No. 3, No. 4) illustrating different configurations of a parapet and its relationship to the ground level. No. 1 shows a simple horizontal parapet. No. 2 shows a sloping parapet. No. 3 shows a more complex sloping parapet with a ditch. No. 4 shows a parapet with a ditch and a specific point of intersection.

Fig. 14.

Again (fig. 14, No. 4) in this figure A is higher than B, or than C, which is the lowest of all; and if H still represents the difference of level of A and C, and $h$ the difference of level of A and B, $AD = N - h - \frac{d}{D+d} \cdot (H-h)$ . . . (3); and, of course, so far as concerns the height alone of the parapet, this is the most favourable condition of all.

Any other case is easily resolvable by one or other of the formulae;—thus, when A and C are on the same level, and B higher than A, H becomes O, and No. 2 becomes $AD = N + h - \frac{d}{D+d} \cdot h$ .

And in No. 3, if B be higher than A, it becomes positive, and $AD = N + h - \frac{d}{D+d} \cdot (H+h)$ . . . (4); or if $h$ be 0, A and B being on the same level, $AD = N - \frac{d}{D+d} \cdot H$ .

In equation (4), if the station C, though below A and B, falls between the horizontal line drawn through A, and the line BR or BA be prolonged till it cuts the surface of the ground, sloping from B towards D, then $\frac{d}{D+d} \cdot (H+h)$ is less than $h$ , and AD is greater than N; but should C be below the line BR, then $\frac{d}{D+d} \cdot (H+h)$ is greater than $h$ , and AD is less than N; or, in other words, if the line of defilade passing through B meets the ground at R within the prescribed limits of defilade, or the effective ranges of musketry and artillery, which may be now assumed as 500 yards for the first and 1000 yards for the second, if the point C be above that line the parapet at A must be made higher than the normal height, and if below it may be made lower. A comparison between the numerical results attached to equation (2) will exhibit the great disadvantage, to the defenders of simple lines, of having any ground near to their own moderately elevated, and care should be therefore taken either to occupy the ground or to throw back the lines op-

posite such eminences as far as possible, and should it have the character of a ridge, to bring some portion of the fire of the line to act in the direction of its length. The space AB to be defiladed must depend upon circumstances, but the minimum to allow for a safe communication for the troops behind and actually defending the parapet ought not to be taken below 30 feet, and where troops are required to be drawn up behind the parapet at 90; but in cases of double lines or of inclosed works the distance must of course vary, as the object will then be to protect not only the troops nearest to the enemy from a direct fire, but the troops arming the more distant parapet from a reverse fire. In assuming the normal height as 8 feet, on the supposition that the fire might proceed from mounted soldiers, a condition is adopted which is not generally likely to occur in the attack of intrenchments; if, however, the normal height were assumed at 7 feet, the space behind the parapet must be very imperfectly defiladed, as the trajectory of the ball, being in its descending curve, will come to the ground at a much nearer point than in the original supposition of a straight line of trajectory; and hence it is desirable to adhere to the normal height of 8 feet. In equation (3), and in one case of (4), as explained, the height of the parapet becomes less than N, but should the diminution extend so far as to reduce the height of the parapet below 7 feet, the absolute relief should be restored to its proper amount, or to 7 feet, by excavating the ground behind the parapet, or, in other words, forming a terreplein below the level of the plane of site. In a similar manner, in respect to equation (2), and in one case of (4), where the parapet becomes greater than N, it would be very inconvenient to augment the height above 12 feet, and it is preferable therefore to excavate behind the parapet, whenever the defilade requires so great an increase of height.

In the preceding observations the parapet has been considered as forming a simple continuous line, deriving its defence solely from its own direct fire; but such a condition would most frequently be found inapplicable, even as regards form, in consequence of the natural inequalities of the ground, and, with few exceptions, unsatisfactory, as regards defence, in consequence of the imperfect operation of direct fire from the top of a parapet, which can only be brought to bear upon some external line, and must therefore leave the foot of its scarp unseen and unprotected, after an advancing enemy has come within the limiting line of defence. A fire, therefore, so directed as to take the enemy in flank has been adopted, and a line or work is therefore said to be flanked when some portion either of its own parapet, or of the parapet of another work, has been so arranged that the fire from it shall take an enemy advancing towards the other portion in flank. In lines of intrenchments this arrangement leads to a bent line, having angles projecting towards the country called salient angles, and angles retired from the country called re-entering angles; and it is evident that in this arrangement (fig. 15) the lines AB and AC, which are flanked by BD, CD, do in their turn flank BD and CD, and that flanking defence may therefore be called reciprocal defence, a term which more accurately defines its object and value.

Referring back, then, to the subject of defilade, it is evident that a bent line of this kind affords more facility for defilading than a straight one, as it is often possible so to arrange the position of the angles that the salients shall occupy high points of ground, while the re-entering angles though placed on lower shall be compensated for this defect by being further removed from the commanding ground of the enemy.

Whilst a simple straight line has the disadvantage of depending for its defence solely on direct fire, it has the advantage of not being exposed to a fire from the enemy so directed as to sweep along its whole length from one end to

the other, a fire which is called enfilade fire, and is necessarily very destructive, as it produces the same effect in

Fig. 15.

attack as a flanking fire in defence, by taking the defenders of the line in flank. To guard against this evil, should it be indispensable to take up a position in front of ground of a superior command, the long lines AB, AC should at least be so directed that their prolongations should fall in low ground at EF, and not as they would do in the case of AB', AC, on the high ground at E'F'; and of course, if possible, and where the high ground is not continuous, that the prolongations of both short and long lines should fall on the low ground between the commanding eminences, an arrangement which will be more especially beneficial should the low ground be marshy or otherwise difficult of occupation by an enemy. Such observations as these can only be suggestive, since no fixed rules can be laid down for an engineer in such

cases, as he should look at his ground and adjust his works so as to make the most of the natural advantages it presents, and to neutralize, as far as possible, the ill effects of any disadvantages it may possess. To determine the height of the parapet by defilading in the manner stated, it is necessary to have a correct plan of the ground, and to know the exact levels of the points A, B, C, in every case; but the defilading may be effected by levelling poles or boning rods where there is no such plan. In this case the inner boundary of the ground within the parapet required to be defiladed being staked out, a boning rod of 7 or 8 feet high, according to the intended normal height of the parapet, should be placed at BC, on the staked-out line, and another of equal height on the commanding point or ground, fig. 16, supposed to be either at or within the range of the projectiles against the fire of which the work is to be secured. A rod about 12 feet high is then fixed at A, and a cross-piece or marker, as in levelling staves, is raised up or down until it meets the point where the visual line from the top of B to the top of A intersects the pole at A; so that this operation is simply the mechanical determination of the height obtained in the other method by calculation. If it be required to defilade the whole space between two parallel lines, or that included between the two lines forming the salient angle in fig. 15, it is evident that the work must be defiladed from both sides, and further, that the soldiers standing on the banquette of one line should be secured from the fire of the ground in front of the other, or from the fire called "reverse fire," as taking them in rear. This is effected by placing a mound of earth or traverse between them, and determining its height as well as the height of the parapets in the following manner:—On the commanding point C is placed the boning rod CD of the normal height, and

Fig. 16.

another BE, at B, or at the position of the traverse of the same height; then the height of the crest of the parapet of A is determined by the intersection of the visual line from D to E with the pole fixed at A, at the point $a$ , which is here high, as C is so much higher than A. See preceding rules and equations. In like manner a pole of the proper height being fixed at the extent of range on the opposite side at C, the visual line from D' to E determines the height of the parapet of A' at $a'$ , which is much lower than the parapet of A, as A' and B' are nearly on the same level. Now, to defilade the banquettes, and to determine the height of the traverse necessary for that purpose, set up on the banquette of A a pole $bb'$ of the same height as CD, CD', BE, and the visual line from D to $b$ determines the height of the traverse at $f$ , which is necessary to secure the banquette of A from the reverse fire of C, whilst the visual line drawn from D to $b'$ determines the height of the traverse sufficient to protect the banquette of A' from the reverse fire of C. The application of these principles is shown in reference to a work formed of two lines (or faces as they are called), terminating in a salient angle, by fig. 17; whether that work is connected with a line of intrenchment as in a redan, or is detached as in a ravelin and other outworks, or forms part of a peculiar system or arrangement of works as in the tenaille system of Montalambert, called by its author the angular system; terms and works which will be hereafter more fully explained. Here the commanding point is supposed to be at M, and to secure the defenders of the face AB from a reverse fire,

it is necessary to interpose the traverse $ed$ , called from its object a parados. The length of the traverse $ed$ is determined by the line MB, beyond which it should project

Fig. 17.

sufficiently to give ample security to a space about 50 feet wide behind the parapet. At the other end, the traverse is not carried up to the salient angle, as it would interfere with the communication, but is completed by $ba$ , perpendicular to the other face, by which arrangement the space within the salient and the banquette are left free. The two lines $MaB$ , and $Mef$ , will be directed to points raised above the banquette by the normal height assumed, whether 7 or 8 feet, and thus determine the height of the traverse. It may, however, happen that the commands are so situated as to produce an enfilade fire along both the faces AB, AB'; fig. 18. In this case a small work is formed DAD' in connection with the parapet, by drawing lines parallel to the crest of CB and C'B' at a distance from it equal to the breadth of the banquette, and then determining, in the manner explained, the height of A necessary to defilade a certain length of the banquette of CB and C'B' sweeping

Fortification. it, and assuming the greatest of the two as the height of the parapet at A. This work is called a bonnet; and when the height necessary to defilade the whole of one or both faces is found to exceed 12 feet, the height of A should be restrained to that limit, and traverses, T, T', T'' be placed at such distances as shall cause a complete defilade without exceeding the height of 12 feet.

Fig. 18.

The internal space may frequently be sufficiently defiladed by raising the salient portion of the parapet without disturbing the line of direction of the crest; but in that case the banquette of the two faces would not be covered from the enfilade fire, and hence the necessity of a bonnet. The increased height of the parapet of the bonnet renders

Fig. 19.

it necessary to adopt two banquettes b, b', one below the other, and each provided with steps to facilitate ascent, fig. 19. The operation of defilading may be also effected by planes of defilade; as, for example, if the line which marks out or limits the space to be defiladed be first drawn, and a plane be supposed to pass through a line either 6 ft. 6 in. or 8 ft. (or whatever height between these may be assumed as the normal height N) above the limiting line, and through a point the same height above the commanding point, this plane will determine the height of the parapet, the crest of which will necessarily be in it. Practically it may be done thus: On the boning rods marking the ends of such portion of the limiting line as can be included in one operation, mark the normal height N considered necessary, and then remembering that a vertical plane through the boning rods would necessarily intersect the defilading plane in a straight line, place one edge of an equilateral-triangular frame of wood in the intersecting line by directing it to the marks on the boning rods, and then attach the frame in that position to an intervening rod. The base of the triangle will

now be in the defilading plane, and by moving the triangle on the base as a hinge until the mark on the boning rod at the point of command is just seen along the surface of the frame, it is evident that the triangle itself will then be in that plane also. Fixing the frame in this position, it is only necessary to look along its surface in any direction in order to mark on the boning rods set up on the line of the crest of the parapet the necessary height at each point.

Where the parapet is continued not only on the flanks but also in the rear, so as to form an enclosed work, it may often be necessary to defilade it in various directions as in fig. 20. Where two traverses or parados cross each other, they must, of course, be so placed that they shall not only complete the defilade of the whole interior space of the work, but secure from reverse fire the banquette on each side, the normal N being therefore, at least, 6 ft. 6 in. above the banquette. Where traverses of this kind become necessary, the engineer must take into account the space they will occupy, and plan his work accordingly; and should he be able to render the difficulty of attacking one side of his works very great, he may so construct one or more of the traverses that they may be used as retrenchments, and thus increase the means of defence; for example, S being the salient of greatest strength, be might be first defended, and then be.

This subject has been enlarged upon because it is one of the most important in engineering, as the safety of a long line of works may be endangered by defective defilading. Though exhibited here in a practical form, it depends essentially on geometrical principles, and instruction therefore in descriptive geometry is now considered essential in all schools of military engineering.

Having determined the relief of the crest of the parapet in reference to the plane of site, all the other vertical dimensions depend upon it, as shown in several of the preceding figures; whilst the horizontal are regulated either with regard to the slopes required to ensure stability, or the thickness necessary to resist the enemy's missiles. For example, it has been determined that the penetration at a mean range in common earth, after having been dug up and well-rammed, and the thickness for security, are as stated below:—

Weapon.	Penetration.	Required thickness for security.
Musket.	1 ft. 6 in.	3 ft.
6-pounder.	3 6 to 4 ft. 6 in.	6
9 "	6 6 to 7 6	9
12 "	8 6 to 10 0	14
18 and 24 pounder	11 6 to 13 0	18

But as neither the 18-pounder nor 24-pounder is now often brought into the field, the thickness of parapet has been usually assumed to be 14 ft. In the Austrian service, in which, as in the Russian, the 18-pounder is a recognised field-gun, it is usual to allow the following thicknesses:—

	Feet.
For defence against Musket balls .....	4-3
" 3-pound shot .....	4-6
" 4 and 6 pound .....	8-6
" 8 and 12, and 7 and 10 pound } howitzers .....	13-0
" 18-pounder shot .....	16-8

With light, sandy, or gravelly soil, or, when tamping can only be imperfectly performed, a greater thickness ought to be allowed; and, as the presence of a wide and deep ditch must always materially strengthen the work before which it is placed, there can be no other reason than want of time, want of men, or difficulty of ground,

Fig. 20.

for reducing the thickness of the parapet below 14, or at the utmost 12 feet. If wood be used, the same authority gives us the necessary thickness for resisting musket balls at from $5\frac{1}{2}$ to $6\frac{1}{2}$ inch; against 3, 4, or 6 lb. shot, $3\frac{1}{2}$ to 4' 11"; against 8 and 12 lb. shot, or 7 and 10 lb. shells, 4' 9" to 5' 4"; and against 18 lb. shot, 6' 6". Brick walls from 2' 8" to 3' 3" thick; and rubble walls from 3' 3" to 3' 10" will resist field-guns. For forming the parapet under peculiar circumstances of difficulty the engineer will avail himself of every fitting substance which may be at hand; such as bags of wool, mattresses, fire-wood, manure heaps, as well as fascines, either by themselves or packed in gabions. Of these latter substances the resistance is not great, the penetration in wool being double that in rammed earth, and the strength of fascine works being rapidly diminished by the speedy fracture of the branches when exposed to a sharp fire.

With these data it will be easy to regulate all the dimensions of the parapet, the height of its crest, or the relief of the work, having been first established. Thus the plane of the banquette or step on which the men stand, when firing over the parapet, should for convenience be 4' 3" below the crest, and on no account should exceed 4' 6". The breadth or tread for a single rank should be 3', for a double rank 4' 6"; the surface should slope backwards 2 or 3 inches in the 3—3 or 4 $\frac{1}{2}$ inches in the 4' 6", so as to discharge water freely and keep the banquette dry; the base of the interior slope of the banquette up which the men mount should be twice its height; if the height of the parapet exceed the normal height, it will be desirable to form two treads or steps to the banquette, the lower about seven feet below the crest, so that one rank of men may stand there whilst reloading the muskets of those in advance of them; or, to adopt steps with a rise to each of 1', and a tread of 1' or 1 $\frac{1}{2}$ ', sloping slightly to the rear, by which arrangement the necessary excavation of the ditch will be diminished, and less of the interior space occupied. The interior slope of the parapet should be 1', or a base of 1' to 4' of the height, and should never exceed a slope of 1 to 3—the superior slope or plongée, of the parapet, by which the fire is directed towards the point on which it is to act, should not be less than $\frac{1}{2}$ , nor more than $\frac{1}{4}$ of its thickness, and in service is generally made $\frac{1}{2}$ ; but as the increase of the slope facilitates the destruction of the crest, it should be kept as small as possible; and it is usual on the continent to retain the angle of the crest as a constant quantity, at 100°, and hence to increase the base of the interior slope as the plunge increases, and vice versa; but this is not satisfactory, since the height of the soldier's shoulder remaining constant,

whilst the direction of the prolongation of the line of plunge varies, the fire will not be always in the true direction; and it seems therefore preferable to keep the base of the interior slope as small as possible, and to make the top of the parapet at the crest horizontal for one or two feet, commencing the plunge at that point, and bringing it inwards in proportion to the increase of plunge. This flat space will facilitate the use of sand bags (bags filled with earth), which are sometimes so arranged on the crest of the parapet as to form loopholes for the musketry, whilst they add to the cover of the men; the base of the exterior slope of the parapet is equal to its height, in earth of a medium tenacity, so as to form an angle of 45°; and in some particular cases where the materials would naturally stand at a steeper slope, it may be made $\frac{2}{3}$ . The bases of the slopes of the scarp and counterscarp of the ditch, as being cut in undisturbed ground, need not exceed $\frac{1}{2}$ of the depth as a general rule, though occasionally in very loose ground the slopes will require to be as gradual as in the exterior slope, or slope of made ground, in order to insure stability. Where steeper slopes are deemed indispensable, the earth must be supported in place by a retaining coating (or wall) called a revetement, which may be formed of fascines (long cylindrical bundles of faggots), hurdles, sods, planks, clay pudding, and, in interior works, of sand bags. The base of the interior slope of the glacis should be equal to its height, and the exterior slope have a plunge of 1 foot in 12. The command of the crest of the parapet over that of the glacis should be such that an assailant, having arrived on the crest, should not be able to fire into the interior of the work: a condition which requires a command over the glacis of 5 $\frac{1}{2}$ feet, so that with a parapet of 7 feet high the maximum height of glacis would be 1 $\frac{1}{2}$ feet. The minimum height of the glacis is determined by another condition, viz., that the fire from the parapet should be in a plane not more than 2 feet above the surface of the glacis; and in no case should the plunge or slope of the glacis be greater than that of the parapet. An advanced glacis is sometimes adopted either for rendering the cover more effectual, or to occupy a favourable line for first opposing the progress of the enemy. Fig. 21 shows this arrangement, $g, g'$ being the first or ordinary glacis, and $g'', g'''$ the second or advanced glacis. The slope of neither glacis should be such as to withdraw the assailants from the grazing fire of the parapet, and if it be not possible to extend the slope of $g'', g'''$ so far as to keep it in the prolongation of the line $C-g'$ , it should be at least so arranged that no point of the slope should be more than 2 feet below that line or the plane

A technical cross-section diagram of a fortification's glacis system. It shows a central ditch with a parapet on its left bank. To the right of the ditch is a glacis. The diagram illustrates the 'ordinary glacis' (g, g') and an 'advanced glacis' (g'', g''') positioned further to the right. A line of sight or 'plunge' is shown extending from the parapet over the glacis. Various points are labeled with letters: C, g, g', g'', g''', and Z. The diagram uses hatching to represent earth and other materials, and dashed lines to indicate geometric relationships and slopes.

Fig. 21.

corresponding to it, namely, the plane passing through the crest of the parapet and the crest of the advanced glacis. To form the advanced glacis, the slope at $g$ is prolonged below the surface of the earth to $g'$ , the excavation supplying material for the raised glacis. When it is intended that the defence of this advanced glacis shall be derived solely from the parapet, either an abattis or rows of stakes may be placed immediately behind it, so as to stop the advance of the enemy when at the point of maximum exposure, but such glacis may often assume the character of successive intrenchments, and be defended with vigour and success.

This figure will be again referred to when treating on defence by mines. The height or relief of construction of the parapet having been determined by the amount of cover required, and the thickness by the nature of projectile expected to be brought against it, the whole profile or section has necessarily been completed on the principles pointed out, and the bulk, therefore, of earth contained in any portion of the parapet will be equal to the area of the mean or average profile multiplied by the length of that portion. Now, this earth must be obtained from the ditch, and hence the dimensions of the latter depend on those of the former,

Fortification. whilst at the same time the volume of any portion of the excavated ditch will also be equal to its mean section multiplied by the length of that portion. If, then, $P$ represent the area of the mean section of this portion of the parapet, $D$ the area of the mean section of the corresponding portion of the ditch, and $L$ the length of this portion, $LP$ should be $= LD$ , providing the earth of the excavation were of the same bulk as after it; but such is not the case, and after having been broken up from its previously closely packed condition, it is found that the "remblai" or earth built up exceeds the "deblai," or earth excavated by a co-efficient varying with the nature of the soil, being in sandy soil nearly 0. Thus if $\frac{1}{m}$ represent the coefficient, it is in sand 0; in earth of medium tenacity $\frac{1}{2}$ ; and in very strong and naturally compressed earth $\frac{1}{3}$ ; so that to render the earth of the ditch just equal to that of the parapet, the above equation should be $LP = L \left( D + \frac{1}{m} D \right)$ and $P = D + \frac{1}{m} D$ , or $D = \frac{m}{m+1} P$ . As, however, the earth resulting from this excess, even allowing for the greater length of the ditch in polygonal works, will be required for forming the glacis, or for making up the banks in the salient called "barbettes," and intended for raising guns sufficiently high to fire over the parapet, the dimensions of the ditch may be safely estimated without reference to the excess, as follows:—

Let $x$ be the breadth of the bottom of the ditch, and $y$ its depth; and let the sum of the bases of the slopes of the scarp and counterscarp be represented as a function of the

depth by the fraction $\frac{r}{s}y$ ; then $x + \frac{r}{s}y$ will be equal to the

breadth of the ditch at top, and $D = \frac{y}{2} \left( x + x + \frac{r}{s}y \right)$

whence $x = \frac{D}{y} - \frac{r}{2s}y$ , and $y = \frac{s}{r} \left( -x + \sqrt{x^2 + \frac{2}{s}rD} \right)$ .

Now as the defensive object of the ditch requires that it should be both deep and wide enough to form a decided obstruction in the way of an enemy, the width ought not to be less than 18 feet, whilst the depth should have no other limit than that arising from the difficulty of raising the earth which makes 12 feet about the maximum. Taking

then $y = 12$ , $\frac{r}{s} = \frac{3}{2}$ , and $D = 108$ superficial, $x = 9 - 9 = 0$ ,

and the width of the ditch therefore $= \frac{2}{3}$ of $12 = 18$ ; the ditch being triangular.

Assuming a profile area of 70, corresponding to a parapet 7 feet high and only 6 feet thick, and making $x = 0$ for

a triangular ditch, $y = \sqrt{\frac{2}{r}D} = 9 \cdot 7$ , and the width of the

ditch $= 14 \frac{1}{2}$ feet: with a profile area of 116 feet corresponding to a parapet $7 \frac{1}{2}$ feet in height and 12 feet thick, the depth of the ditch, if triangular, is $12 \frac{1}{2}$ feet and its width $18 \frac{3}{4}$ ; so that this profile appears about the maximum for a triangular ditch with a profile area of 163 feet, corresponding to a parapet 8 feet high and 18 feet thick. With a banquette $4 \frac{1}{2}$ feet wide a triangular ditch would give $y = 14 \frac{3}{4}$ feet, so that such a form would be inconvenient; but taking $x = 4$ as the width of the bottom of the ditch, $y$ or the depth becomes $12 \cdot 4$ , and the width of the top of the ditch $22 \frac{1}{2}$ feet—a very well-proportioned ditch.

In the preceding cases the base of slope of the scarp has been assumed as equal to its height, and that of the counterscarp slope as half the height. Should the nature of the soil be such as to require the base to be equal to the height

in both scarp and counterscarp, $\frac{r}{s}y = 2y$ ; and where the soil is sufficiently firm to admit of a base of one-half in both,

$\frac{r}{s}y = y$ . In the first of these cases even the large profile area

last named may be made triangular with a depth of $12 \frac{1}{2}$ feet, and breadth of 25; and in the second a triangular ditch is inadmissible even with an area of 116 feet, as it would require a depth of more than 15 feet; and it could only be used with profile areas up to 85 superficial feet, for which a depth of 13 feet would be required. Before leaving this subject, a few words may be said respecting the "berm." The most effectual scarp in respect to defence is that which forms one continuous plane with the exterior slope, or at least which commences immediately where the other ends, as the absolute relief of the parapet is therefore made a maximum, and there is no berm; but in many cases it would be imprudent to carry the parapet up to the edge of the scarp, as the latter might be easily injured and occasion a fall of part of the parapet, and further, the difficulty of construction would be greatly increased by having no intermediate stage between the bottom of the ditch and the top of the parapet. The "berm" or step between the top of the scarp and bottom of the parapet is made from 2 to 4 feet according to the nature of the ground, and it then becomes possible in most cases to increase the slope of the scarp to a base of $\frac{1}{2}$ or $\frac{2}{3}$ , at least to such a slope as shall bring the prolongation of the exterior slope of the parapet to the base of the scarp. The berm is encumbered with such obstacles as shall prevent an enemy from making it a halting place (see fig. 12). The slope of the counterscarp is usually $\frac{1}{2}$ , $\frac{1}{3}$ , or $\frac{2}{3}$ , when that of the scarp is $\frac{1}{2}$ , $\frac{2}{3}$ , or 1; and it should be added that the bottom of the ditch ought always to slope on each side towards the centre, so as to carry off the water, and that it should be so arranged as to prevent the enemy from collecting together, and reforming his men in the ditch which in all cases of simple lines, without flanking defences, he would do were the bottom left free from obstructions.

APPLICATION OF THE PARAPET IN COMBINED OR RECIPROCAL DEFENCE, CONSTITUTING PARAPET OR FIELD FORTIFICATION.

The parapet has been hitherto considered principally in its character as the simplest element of defensive works, affording at once protective cover to the soldiers behind it and an obstruction to the advance of their enemies; but it is now time to consider the manner in which this parapet may be so arranged as to constitute a series of defensive and mutually defending works. Were the antiquity of an invention to be estimated in reference to an epoch in the social history of any race of mankind rather than to a point in absolute time, there can be little doubt that earth-works would, as might be naturally expected, claim the priority over all other modes of defence. In North America vestiges of circular intrenchments, as well as of works of a more complicated outline, have been discovered, the antiquity of which is unknown; and even now, when a small party of the aboriginal inhabitants have been suddenly encountered by a much greater number of a hostile tribe, they have been known to excavate a hollow space in the ground, and, throwing out the earth, to form around them a circular intrenchment, in which they have defended themselves to the last. In Ireland its ancient inhabitants have left similar relics of their earthen defences, as in Great Britain the Romans have left of theirs; but the further consideration of the value of earthen works, when adopted in the defence of extensive fortresses, will be resumed in a future passage, and they will be considered here only in connection with the arrangements adopted by an army in the field for its own immediate security.

The art of constructing all kinds of temporary works in the field for this purpose is usually called field fortification, a name here replaced by that of parapet fortification. An army intrenched, or fortified, in the field, produces, in many respects, the same effect as a fortress; for it covers a country, supplies the want of numbers, stops the advance of a superior enemy, or, if he chooses to risk a battle, obliges him to engage at a disadvantage. "In a war of march and manœuvre," says Napoleon, "if you would avoid a battle with a superior army, it is necessary to intrench every night, and to occupy a good defensive position. Those natural positions which are ordinarily met with are not sufficient to protect an army against superior numbers without recourse to art. Those who prescribe lines of circumvallation, and all the assistance which the science of the engineer can afford, deprive themselves gratuitously of an auxiliary which is never injurious, almost always useful, and often indispensable. It must be admitted at the same time that the principles of field fortification require improvement. This important branch of the art of war has made no progress since the times of the ancients. It is even inferior to what it was two thousand years ago. Engineer officers should be encouraged in bringing this art to perfection, and in placing it on a level with the rest."

Whenever Napoleon had time and occasion for strengthening his position by field-works, he acted upon the principles recommended in the above extract, as almost all his predecessors had done. In the wars which followed the revolution of 1688, in those of Queen Anne's reign, and during the Seven Years' War, we find the commanders of each period, William III., the Duke of Marlborough, Marshal Villars, Marshal Saxe, Frederick II., and Marshal Daun, practically exemplifying their conviction of the great utility of field-works. A few redoubts saved Peter the Great at Pultowa, and enabled him to gain a decisive victory over his formidable antagonist; and at Borodino, some slight open field-works, thrown up by the Russians, caused the French great loss, and rendered too costly to be of almost any avail the victory which, by incredible efforts of gallantry, they gained. It has been argued by some, against intrenchments and field-works, that they have oftener been carried than successfully defended, and that hence incommensurate importance has been attached to them. But it should be remembered, on the other hand, that victory in such circumstances has generally been purchased at an expense which rendered it in effect equivalent to defeat; and that a practice which the greatest commanders of ancient and modern times have approved and followed cannot be one of doubtful utility. At Austerlitz, where the contending armies were nearly equal, Napoleon was preparing to superintend the construction of intrenchments when he found himself called upon to receive battle; and in Portugal, the Duke of Wellington showed to what importance the art of the engineer might be turned for influencing, not merely the fortune of a campaign, but the fate of a cause. The lines of Torres Vedras, which formed the ne plus ultra of the powerful French army under Massena, and from which the tide of war was rolled back broken into Spain, were perhaps the most remarkable works of the kind ever constructed.

"Lisbon," says Sir John Jones, "being situated at the extremity of a peninsula formed by the sea and the Tagus, it is plain that if an army be so posted as to extend across

the peninsula, no enemy can penetrate into the city without a direct attack on the army so formed. It was on this principle that the lines covering Lisbon were planned by Lord Wellington. Nature drew the rude outline of a strong defensive position, and art rendered it perfect. A tract of country thirty miles, extending from the mouth of the Zizandra on the ocean, to Alhandra on the Tagus, was modelled into a field of battle; mountains were scarped perpendicularly, rivers dammed, and inundations formed; all roads favourable to the enemy were destroyed, and others made to facilitate the communications of the defenders; formidable works were erected to strengthen and support the weak parts, whilst numerous cannon, placed on inaccessible points, commanded the different approaches to them, and gave an equality of defence to the whole position."² These lines were not continuous and connected works; they consisted of independent forts, redoubts, flèches, redans, batteries, &c., so placed as to command and enfilade every approach, and to support each other by a cross or a flanking fire. The first line occupied a front of twenty-nine miles between the sea and the Tagus; and by means of telegraph intelligence could be conveyed from one extremity to the other in a few minutes; whilst the troops were disposed in masses in the rear of the works ready to move upon any point that might be attacked, by interior communications shorter than any by which the enemy could advance. "The aim and scope of these works," says Colonel Napier, "was to bar the passes, and to strengthen the fighting positions between them, without impeding the movements of the army. These objects were attained; and it is certain that the loss of the first line would not have been injurious, save in reputation, because the retreat was secure upon the second and stronger line, and the guns of the first were all of inferior calibre, mounted on common truck carriages, and consequently immovable and useless to the enemy."³ Both lines occupied a front of fifty miles, on which there were erected one hundred and fifty forts, mounting in all about six hundred pieces of artillery.

Before this formidable position, defended by a double line of works, and by an army massed and ready to move upon any point by interior communications, the French remained five months, wasting their numbers and resources; until at length, finding it utterly impracticable to force any part of even the exterior line, they were obliged to retire from Portugal, closely followed and harassed by the army which they had previously driven out of Spain. Yet though the lines of Torres Vedras were thus perfect in themselves, and though one of the ablest of the French generals and a veteran French army were foiled before them, it is not meant to refer to this system of separate field-works as a model to be followed on all occasions; for whilst the old method of covering a considerable front by a continued line of regular bastions and curtains has been universally condemned by modern engineers, it is nevertheless certain that there are situations where a partial application of continued lines may be most judiciously made. In fact, it is not by any fixed rule, but from the nature of the ground and of the position to be defended, that the species of works calculated to be most useful should, in every case, be determined.

At this point it is necessary to remember, that in any protracted defence, or, indeed, in any efficient defence, artillery must be combined with musketry; and hence that in the arrangement of lines provision must be made for the

¹ Military Maxims of Napoleon.

² War in Spain, p. 124. The French army which invaded Portugal under Massena consisted of three corps, under Marshals Ney and Junot and General Regnier, amounting in all to 66,000 infantry and 6000 cavalry, besides a strong body of the imperial guard, which crossed the Pyrenees after the invading force had commenced its march from the neighbourhood of Salamanca. The force collected to oppose this threatened invasion did not exceed 48,000 infantry and 3000 cavalry, of which about a half was composed of Portuguese levies, yet untired in any general action, and of which a very unfavourable opinion still continued to be entertained. In point of numbers, and still more in the composition of their army, therefore, the French had a decided superiority; but all their advantages were neutralized by the defensive position of Torres Vedras.

³ History of the War in the Peninsula, vol. iii.

Fortification. use of cannon. When it is possible so to place guns that they may bear on definite lines or points, such as a natural ravine, an artificial road or other communication, a line of abattis or other obstacle, the ditch, the scarp, the glacis of some portion of the works which must be passed in advancing to the attack, or the point in front of a salient, it is desirable that they should be preserved in that position, ready to act at the right moment; and hence it is that they should not fire over but through the parapet, and the opening made in the parapet for this purpose is called an "embrasure." It is more usual to make these embrasures in field-works shortly before they are required to be used, so that the parapet may be made quite solid and firm in the first instance, and without the trouble which attention to the preservation of the opening would necessarily occasion in construction. In order to obtain command over a glacis constructed in reference to the exterior slope of the parapet, and yet to insure cover, the parapet must be raised so as to cover the men serving the gun placed on the usual barbette terreplein—(see fig. 22)—which would other-

Fig. 22.

wise fire over the ordinary parapet, and not, as here represented, through an embrasure. The section shows by dotted lines the difference of level between the terreplein of the gun and the plane of the banquette of the ordinary parapet. The dimensions of the embrasure are determined on simple principles—the interior opening or neck is made only 20 inches wide to avoid unnecessary exposure of the men, and the exterior opening is made half the thickness of the parapet, measured along the ridge line of the exterior slope; (see fig. 23). When the guns are intended to flank the ditches, or to fire along a ravine, or the crest of a natural scarp, which fulfils the function, as an obstacle, of the ditch, the embrasures are cut in the ordinary parapet, and the guns stand on the natural terreplein of the work, as stated above.

The portion of parapet left below the embrasure is called genonillère, from genon, the knee; and for field-guns should be 3½ feet high; the portion between two embrasures is called merlin, from the Italian merlone, a battlement; the bottom of the embrasure is called its sole; and in the same manner as has been suggested in respect to the superior slope of the parapet, it should be horizontal for the first four feet from the neck or interior opening, and then slope downwards as much as may be necessary to attain the amount of depression required in firing. The direction of the embrasure depends on the intended direction of the line of fire, and is either perpendicular to the crest as at a'b, or oblique as at ma (fig. 23). In the latter case, should the obliquity be very great, or exceeding 70°, the crest of the parapet must be made re-entering, as at oi, so as to strengthen it near the neck, and to enable the gun carriage to be brought up square to the parapet; oP should be at least 8 feet; the sides of the embrasure are called checks,

and should be rivetted either with planks, with sods, with fascines, or with gabions (hollow cylinders made of wicker

Fig. 23.

work, and filled with earth). In fig. 24, on the left, at B, a direct embrasure is seen cut straight through the parapet; and on the right at A, an oblique one, both being intended to enfilade the ditches opposite them; and it will be observed that, from the obliquity of the right-hand embrasures, the interior of the work becomes so much exposed, that a traverse, T, behind the embrasure, becomes necessary. Barbettes are also shown in this figure—one at the salient at D for four guns, and another at C, perpendicular to the

Fig. 24.

face or branch, for two. The terreplein of the barbette should be from 3 to 3½ feet below the crest of the parapet; its height from front to rear from 18 to 20; and its breadth, for a single gun, from 15 to 18, according as it may be necessary to fire more or less obliquely; and a breadth of 12 to 15 feet should be added for every additional gun. To add to the lateral sweep or range of the gun, without diminishing the banquette, or, in other words, the musketry fire, the barbette may be made wider in the rear than in front. In proportion to its magnitude should be the number

Fig. 25 a.

of "ramps," or slopes of approach; as, for example, at C only one, at D three. The ramps should be from 8 to 9 feet wide, and their slope should have a base equal to 4 times the height of the barbette. The lateral slopes of the barbette and of its ramps should be rivetted whenever it is possible to obtain sods, fascines, or hurdles, in order to eco-

nomize space in the work, as the base of the slope may be then reduced to $\frac{1}{4}$ or $\frac{1}{5}$ the height; more generally they are left unrevetted, with slopes of $\frac{1}{2}$ . The terreplein of the barbette may require, as at C, to be covered in flank by a traverse. The mode of constructing a barbette in a salient is exhibited in fig. 25 a.

At any point g of the face AB raise a perpendicular gh, either 18 or 20 feet in length, to include the amount of re-

coil; at the point $h$ thus determined raise a perpendicular to $gh$ and prolong it to its intersection with the other face $AC$ at $E$ , then setting off $AE$ on the other face equal to $AE$ . On the capital $AD$ , set off a double perpendicular at any point $i$ , prolonging it both ways, and making $ik$ and $il$ each at least equal to $\frac{1}{2}$ feet to represent the half breadth of the platform on which the gun-carriage is intended to stand and move; through the points $k$ and $l$ draw parallels to the capital, cutting the faces on the points $m$ and $n$ ; join $m$ , $n$ , and parallel to the line $mn$ draw the line $OP$ at 18 or 20 feet distant from it, when $m$ , $n$ , $P$ , $O$ , form the platform. Join $FO$ and $EP$ , and $AEPOF$ will represent the contour or trace of the barbette. The manner in which the crest of the parapet is formed above the salient $A$ , and the mode in which the firing may be effected in directions perpendicular to the faces, as well as in the direction of the capital, is shown in fig. 25 b.

Fig. 25 a.

In the case of a partly sunken parapet, in which the portion above the banquette is raised above the plane of site, and the portion below the banquette excavated as in fig. 26, the barbette constructed in the hollow portion will enable the gun to fire over the parapet; and it should be protected by forming a bonneted embrasure, which may be sometimes made large enough, as here represented, to hold two guns. It need scarcely be added that an engineer ought to be ready in adapting any of the expedients here briefly noticed to the circumstances of any particular case,

Fig. 26.

and that a mind stored with resources against any possible casualty is one of the highest endowments of a really good officer. It must be obvious indeed that even a limited knowledge of the art of war opens a wide field for the exercise of the talents and resources of engineers in field fortification; but the possession of a military coup-d'œil, or of that

intuitive judgment which comprehends at a glance the true bearing or character of objects as well as events, is necessary to enable them to convert theoretical stores of information to the best practical uses. In passing through a country, it requires an experienced eye to seize quickly on whatever it presents calculated to prove advantageous or disadvantageous to an army destined to attack or defend it; to appreciate the value of villages, stone-inclosures, and broken ground; to know where to dam up rivers, to scarp heights, to form abattis, trous-de-loup, and other obstacles; to select the best situations for field-forts and redoubts, and the best sites for batteries; and to arrange all the defensive means employed, with reference to the number of troops destined to act upon the different parts of the line, so that the movements of the defenders may not be obstructed or retarded, and the communications throughout may be short and easy. The variety of ground, however, upon which military operations are for the most part carried on, precludes the possibility of laying down fixed rules in regard to this subject; the accidents of ground, and the peculiar circumstances of each individual case, must, as already observed, determine the extent and description of the works to be constructed, as well as the obstacles most proper to be formed for retarding, if not obstructing, the advance of an enemy.¹

At the same time, though the observance of fixed rules be impracticable, general principles are of universal application; and certain maxims founded upon them hold equally good in regard to the construction of field-works as in that of the more complicated works of a fortress. These are, first, that the works to be flanked must never be beyond the range of the projectiles used in the works flanking them, or in other words the length of the lines of defence never exceed the effective range of musketry; secondly, that the angles of defence should be about right angles; thirdly, that the salient angles of all works should be as obtuse as possible; fourthly, that the ditches should be as efficiently flanked as is possible; fifthly, that the relief of the flanking works must be determined by the length of the lines of defence; and, sixthly, that in the construction of field-works, reference should not only be had to the direct and immediate obstacles which the work itself is calculated to present to the enemy, and the positive effect of its fire on the approaches to it, but the relative value of the work should likewise be considered with respect to the support it can receive from or give to other works. These principles or maxims are of invariable application.

Field-works are either open at the gorge as in fig. 1, 2, 3, 4, Pl. CCLIX, or inclosed all round as in fig. 5, 6, 7; namely—

Redans, or simple heads.....	fig. 1.
Double redans, or queues d'hironde.....	fig. 2.
Tenilled heads.....	fig. 3.
Bastioned heads.....	fig. 4.
Redoubts.....	fig. 5.
Star-forts.....	fig. 6.
Bastioned forts.....	fig. 7.
Lines à crémaillères.....	fig. 8.
Lines of redans.....	fig. 9.
Lines of tenailles.....	fig. 10.
Lines of bastions.....	fig. 11.
Lines of demi-bastions.....	fig. 12.
Lines broken or with intervals.....	fig. 14.

The first class are of the simplest kind of field-works, and serve as a mere cover in front of avenues, bridges, (see fig. 13), causeways, and the like; but being quite open at the gorge, they are only suited for defence when their extremities rest on rivers, or obstacles which prevent their being turned, or when within the full sweeping fire of works

¹ Shaw's Course of Field Fortification, p. 9, et seqq. Much assistance has been derived from this useful work in the compilation of this article, as well as from the admirable Treatise on Field Fortification by Fischmeister, translated by Rieffel into French, the figures of which have been freely used.

Fortification. in their rear. To increase the strength of a redan, its faces are sometimes broken into a kind of flank, as in fig. 1, Pl. CCLIX. In the double redan, or queue d'hironde, fig. 2, the re-entering faces defend each other; the tenuilled heads are used in situations which require a greater extent of front; and the bastioned heads are also employed in similar circumstances. See fig. 3 and 4.

Redoubts are works closed on all sides; they are constructed of a square or polygonal figure, but most commonly square, as, when of this form, each front can furnish a strong perpendicular fire. Provision should be made for defending the ground before the angles, which, however, are sometimes rounded or cut en crémaillère, so that a fire may be delivered from them. See fig. 5.

Star-forts were proposed in order to remedy the defects of redoubts having the ground before them undefended by a flanking fire, so that a cross fire might be delivered from the adjacent sides. But according to Jomini, "star-forts are the very worst description of fortification; they cannot have flanks, and the re-entering angles take so much from the interior space that it is impossible to place troops and artillery in them sufficient for their defence;" an opinion confirmed by the practice of Sir Richard Fletcher and Sir John Jones in the construction of the lines of Torres Vedras, where the trace of the redoubts was made subservient to the conformation of the ground, to the object in view, and to the protecting them as much as possible from the fire of the enemy's position.

In bastioned forts, fig. 7, the flanking defence obtained for the ditch is nearly perfect. As bastioned forts are only constructed in cases of great importance, no labour or expense should be spared in the formation of such works.

Forts with demi-bastions, fig. 12, are objectionable, as the ditches are only defended by an oblique fire of their faces. The parapets of all these works should be of sufficient thickness to resist the fire of the heaviest guns that can be brought against them. In some cases, however, the parapets need only be strong enough to resist the fire of light field-guns, whilst in others it will be sufficient if they serve as a cover to the men within them against musketry. The latter kind is generally that which is thrown up in an evening after taking up a position, and which, if the army does not move next day, it may be considered as necessary to strengthen in some parts, according to circumstances.

Continued lines, or connected works, are resorted to in order to inclose the front, or to connect important works or forts. The most simple tracing is that of redans joined together by curtains (fig. 9); but as the ditches of these curtains can only be defended by an oblique fire from the faces of the redans, this defect may be remedied by breaking the curtains so as to form nearly right angles with the faces of the redans, in which case they are called lines of tenailles.

Lines en crémaillère have long faces, with flanks perpendicular to these, in order to defend their ditches. When the faces can be directed towards ground upon which it is impracticable to establish enfilading batteries, the construction is considered as good.

Bastioned lines form the strongest trace which can be given to continued lines, when the ground will admit of its adoption. A perfectly regular trace is only suited for level ground. The ditches in field-works are often sloped en rampe towards the adjoining flanks, in order that the deblai, or quantity of earth excavated, may not exceed the remblai, or quantity contained in the mass of the rampart or parapet, a circumstance which often occurs in field-works, where there is seldom any rampart, and only cover sufficient for the defenders.

Lines with intervals. Fig. 14 shows the general trace of lines of this kind. The salient works should never be beyond the range of musketry from the re-entering works,

and the angles of defence between the two lines should be as near as possible to right angles.

Têtes-de-pont, or bridge-heads, are works generally open at the gorge, and whose flanks rest upon a river, in order to cover one or more bridges. The best situation for these works is the re-entering sinuosity of a river. As têtes-de-pont, fig. 13, are usually constructed for the purpose of enabling a retiring army to cross a river in order, and to check an enemy pressing upon it, the tracing and profile should be such as to secure a double advantage to the greatest extent possible. In Sir Howard Douglas's able work on the Construction of Military Bridges will be found much valuable scientific information upon this important subject.

The obstacles which are usually added to field-works, in order to render the approaches more difficult to the enemy, such as palisades, barriers, abbatis, trous-de-loup, chevaux-de-frise, harrowes, and croix-feet, have been already noticed.

For the defence of open towns and villages, the following methods, recommended by the French minister of war in 1814, are considered as the best that have yet been suggested: "To admit of a town being advantageously intrenched, it is necessary that it should not be commanded within any short distance, that the houses should not be of a construction easily set on fire, and that its extent should not be out of proportion to the means and time at the disposal of the defenders. The first thing to be done is to clear the approaches to the town, by levelling houses, hedges, shrubberies, and whatever may favour the assailants. Wood ought to be cut two feet from the ground, that it may serve to impede the advance of the enemy without masking the fire of the defenders. The next object is to form or complete the inclosure round the town. For this purpose advantage is taken of buildings, walls, and fences applicable to the defence. The openings which remain must be closed by palisades, stockades, or ditches strengthened by abattis. All streets leading out of town must be barricaded. The barricades must be sufficient to resist field artillery, and high enough not to be easily got over; and they ought to be flanked by loopholing the neighbouring houses. When pressed for time, carts filled with dung and the wheels taken off, sand-bags, bales of wool or cotton, and furniture taken from the neighbouring houses, all form good barricades. If there should be any old castle, church, or large substantial building, it should be converted into a keep, by blocking up useless entrances, loopholing walls, and surrounding them by a ditch or abattis. If a town is situated near a stream or river, by which part of it may be covered by inundations, this should never be neglected."

Villages are intrenched on similar principles, and being generally surrounded by gardens with live hedges, the latter may be made use of in forming the lines of defence. If there should only be sufficient troops to defend part of a village or town, a part only should be intrenched and separated from the rest by means of carts and barricades. If there are very few houses, it may be necessary to confine the defence to the church or churchyard, which may in all cases serve as a sort of keep.

The destruction of bridges. Nothing is of greater consequence to a retiring army than to be able to destroy the bridges in its rear, in order to retard the advance of the enemy. Its safety, nay even its existence, may depend upon the success with which this operation is performed. In order to destroy a stone-bridge, a trench in the form of a cross is made in the crown of the arch, the branches of which are about ten feet in length, and sunk to the top of the arch-stones. One hundred and sixty pounds of powder are placed in each cut or trench for an arch three feet thick, strong planks are then laid over the powder, and the whole being well covered with rubbish, the fire is communicated by means of a saucisson or long powder-hose. Stone bridges are also destroyed by simply cutting a trench about eight-

teen inches deep across the crown of the arch, and placing in it 345 pounds of powder covered in the manner just described. This quantity has been found sufficient to destroy semicircular arches of twenty-five feet in span, and three feet in thickness at the key. Wooden bridges may be destroyed in different ways; they may be pulled to pieces, burned, or blown up. When there is time to take them to pieces, they are unspiked, and the timbers so separated that they may be speedily removed. The best method of burning such bridges is to tar them, and to cover and surround them with fascines or tarred brushwood. When it is necessary to blow up wooden bridges, this may be effected by means of 220 pounds of powder suspended under the superstructure, and fired in the manner above described.

A ford is rendered impassable by throwing in large stones, by sinking boards with spikes standing upright in them, by scattering in it crows' feet, or by placing harrows taken from the neighbouring farms. A low rubble wall may be formed across, so as not to be perceptible above the water; strong stakes may be driven into the bottom, and trees fastened to them; waggons loaded with stones, and the wheels taken off, may in like manner be employed; not to mention a number of other things which may be easily found, and which will answer the purpose equally well. The rendering a ford impassable by such means is only second in importance to the destruction of a bridge, when the enemy whose progress it is desired to retard has either no pontoon-train at all, or has outstripped it by the rapidity of his advance. In this way, much valuable time may be gained on the one hand and lost on the other.

In order to bring a retiring army into the position when the business of intrenching itself would naturally begin, some portions of the subject of defence have been in part anticipated in the preceding passages, and the main line of argument will be now resumed.

The essential characteristic of all works formed of earth is, that the musketry fire, on which the defence must mainly depend, being discharged over the crest of the parapet, the line of fire will be nearly in the plane of the superior slope of the parapet, and perpendicular to the line of its crest; and hence opposite a salient angle, as in the redan, fig. 27, there

Figure 27: A diagram of a redan fortification. It shows a triangular salient point A. A vertical line passes through A, with a point D on the base line BC. The angle at A is 60 degrees. The diagram illustrates the 'dead angle' at the salient point where the line of fire is perpendicular to the superior slope.

Fig. 27.

will be a large space of ground at A, in this case extending over $180^\circ - 60^\circ = 120^\circ$ , not defended by the fire of the work itself, and which is called a dead angle. Opposite re-entering angles, on the other hand, the defect is of a different kind, as the plane of the superior slope or plane of fire passing so high above the foot of the scarp, necessarily leaves it unseen and unprotected, notwithstanding that the two lines theoretically flank each other. The object, therefore, in arranging all field works for mutual defence should be so to regulate their reliefs that the line of defence should terminate at such a distance from the ground as to give an effective defence to the part of the work intended to be flanked. The redan may be considered the most simple form of defensive work, though a portion of straight parapet terminating by short returns at each flank, either in the form of caissons or of regular parapets, may occasionally be combined with defensive works, and is an ordinary form of offensive work in batteries. The redan is open in the rear, and the

line BDC is called the gorge—in this case a straight line—the two demi-gorges BD, CD coinciding in direction. Fortification.

The lunette is a redan to which flanks or lateral wings have been added; and in form, therefore, it resembles a bastion. In Plate CCLIX., fig. 14, lunettes are shown so arranged that the faces of those in rear may flank the faces of those in front; but with respect to the distribution and arrangement of the works destined to form lines of intrenchment more will be said hereafter.

The tenaille is a work the reverse of a redan, as it consists of two lines forming a re-entering angle facing the exterior. It can, from its form, only be used in direct or approximate connection with other works which shall close up or cover the ends of its lines. Either alone or combined with redans it is very commonly used in continued lines of intrenchments. Plate CCLIX., fig. 9, represents a line of redans joined by straight lines, and fig. 10 a line of irregular tenailles, whilst the annexed cut, fig. 28, represents a normal

Figure 28: A diagram showing a line of tenailles. It consists of a series of V-shaped structures (redans) joined together. The diagram shows the re-entering angles at the vertices of these structures, labeled with letters A, B, C, D, E, F, G.

Fig. 28.

line of tenailles, of which the re-entering angles should not exceed $100^\circ$ , and the sides are equal; and cut fig. 29, an

Figure 29: A diagram showing a line of tenailles with irregular sides. It shows a series of V-shaped structures (redans) joined together. The diagram shows the re-entering angles at the vertices of these structures, labeled with letters A, B, C, D, E, F, G, H, I.

Fig. 29.

arrangement of tenailles, with irregular sides, by which a redan, as DEF, is interposed between every pair of tenailles. The line en cremallière, Plate CCLIX., fig. 8, is also derived from a combination of irregular tenailles, and is in many circumstances a very satisfactory arrangement. In selecting between these and other arrangements, including the bastion trace, Plate CCLIX., fig. 11, the engineer must be guided by his judgment on the nature of the ground and the special objects to be attained, and cannot therefore be bound by any rigid rules. A slight consideration, however, is sufficient to show that the combination of regular tenailles, in cut 28, is only applicable to ground in itself regular, an observation which applies to every strictly systematic arrangement in fortification. In almost every case the ground will be more or less irregular, and the works to defend it must be so also. When it is necessary to approach closely to a bank of a river or a ravine, the cremallière line, Pl. CCLIX., fig. 13, is the simplest and best, the short or flanking sides being so placed as to face the probable direction of approach, and next to that the combined redan and tenaille. Of open works, lunettes admit of the most scientific arrangement, as they can be so placed in lines with intervals as reciprocally to flank each other, and thus to form a line of defence very similar to a regular bastioned line. The employment, however, of works open at the gorge must be restricted to positions where the enemy can only approach in front, his advance in other directions having been rendered impossible either by other works, or by obstacles so arranged as to close that particular line of approach to an enemy. In every case it is desirable to take advantage of any peculiarities in the features of the country, and so to modify them as to produce such insurmountable obstacles as may relieve the minds of the defenders from apprehension of danger in that direction, and leave them at liberty to direct their attention more exclusively to the weaker points of their position; but in no case

should even the apparently inaccessible points be left unguarded, or rather unwatched, as an enterprising and skilful adversary will sometimes surmount difficulties which had appeared to others insurmountable. As such naturally defended points in a position can only be looked upon as exceptional advantages, it is evident that works left entirely open at their gorges would be liable to easy and frequent surprise, and therefore prove but imperfect instruments of defence. On this account it has been usual to prescribe as a rule that such works should only be left unclosed when within range of musketry fire from the defences behind them; but it is better to lay down as a fixed principle that in every case they should be secured at the gorge, as the power of driving an enemy out of the interior of such a work when taken is in reality of no value, as his object would not be to remain in its interior, but to turn its parapet to his own uses. The manner in which this is generally done is shown in fig. 30, which is a lunette se-

Figure 30: A plan view of a lunette fortification. It shows a triangular structure with a central ditch and a small rectangular structure at the base. The ditch is labeled 'D' and the central structure is labeled 'F'.

Fig. 30.

cured at its gorge by a loop-holed stockade, which is an obstacle effective against an enemy, and, at the same time, easy of destruction, should be succeeded in temporarily obtaining possession of the works. Any of the obstacles previously described, such as abattis, &c., may be used for the same purpose, but they have the disadvantage of not covering the defenders of the work from the enemy's fire. An engineer in deciding between open works, such as those described, and close works, which will now be described, ought to take into consideration not only the circumstances of ground as regards the security of the work itself, but also the ease or difficulty with which support can at any moment be afforded to its garrison. Open works are not fitted for any position where they are likely to be left to their own resources, even for a moderately short time, as small bodies of men cannot be expected to stand firm against a vigorous attack from an overwhelming force, unless satisfied that support is at hand. Closed works, therefore, in which the parapet is continuous on all sides, can alone be relied upon under such circumstances; and even then the nature of the obstructions adopted in their construction should be such as to afford the garrison a reasonable confidence, that by a vigorous defence they may be able to hold the enemy at bay; for no general should expect to find in soldiers, as a body, that heroism which leads to self-sacrifice without hope. The easy capture of the redoubts at Balaclava, garrisoned by the Turks, is an illustration of this principle; for though it is possible that they might have been longer maintained by French or British soldiers, it would have been unreasonable to expect that their defenders should remain firm until overpowered and cut down by their assailants, which must have been the result had not a supporting force been at hand to relieve them. As general rules, therefore, it may be laid down, that in all detached works the mode and time of relief should be palpable to the garrison; the nature of the constructions such as to inspire confidence in the garrison as to its power of resistance for a reasonable time; and,

above all, that the garrison of such works should be composed of the best, not of the worst soldiers.

Closed works may be either constructed without or with flanking defences; the first, which have only salient angles, being called redoubts, from the Italian ridotto, a place of rendezvous; the latter forts. Redoubts may be either formed as regular or irregular polygons of any number of sides, but the square redoubt is the most simple and the most generally used, see Pl. CCLIX., fig. 5. All such redoubts have the disadvantage of dead salient angles not having any flanking defence; and it is usual, therefore, to place the guns used in their defence, in the salients, so as to fire along the capitals or lines bisecting the salient angles, as well as the dead space in front of them. In like manner the sides should be made to front the probable line of approach, and as shown in one half of fig. 31, which represents a rectangular redoubt, the scarp is sometimes sloped gently down to the bottom of the ditch, and covered with abattis or other obstacles, which can then be seen and defended in front by direct fire. It is indeed impossible to repeat too often that the efficiency of defence in such works must mainly depend on the power of arresting the progress of the assailants just on those points where they will come under the fire of the defenders. The entrance to a redoubt should be made in the least exposed side, and be protected by a parapet traverse behind it, as in fig. 31, where an arrangement of palisades is shown by which the traverse may be connected with the other portions of the parapet, and the entrance be closed by gates or barriers as required. Other traverses may be also constructed in such works either for the purpose of defilade or for affording additional cover to the troops. They may be formed, when the work is sufficiently capacious, of long parallel espallements, with a space between them, which may be even covered over or blinded when it is likely that

Figure 31: A plan view of a square redoubt. It shows a square structure with a central ditch and a small rectangular structure at the bottom. The ditch is labeled 'D' and the central structure is labeled 'F'.

Fig. 31.

the work will be held for a considerable time, and in consequence that a more secure and comfortable lodging will be desirable for the garrison. Magazines for ammunition may be also constructed either against or in such traverses; and fig. 32 (see next page) represents, in plan and section, one which, formed behind a gabion traverse, is isolated from the parapet in front of it. This magazine is sunk partly in the ground, the sides being formed of planks and the roof of strong scantling, forming a ridge in the centre covered first with fascines and then with a coating of two or three feet of earth. Its dimensions are—length 8 feet, breadth 5, height 6.

Having thus generally sketched, as it were, this section of our subject, it is necessary to determine the least size which can be given to redoubts, so as to ensure a sufficient

interior space for the accommodation of the garrison required for the defence of the parapet, remembering that in works not provided with flanking defences the whole parapet, unless secured in part by some insurmountable natural obstacle, must be defended.

Fig. 22.

A general formula may be easily obtained for determining the least regular polygonal trace in the following manner:—Let $x$ be the side in feet of any regular polygon, $n$ the number of sides, $A$ the interior surface reckoned from the foot of the banquette, $y$ the number of men forming the garrison, $f$ the number of linear feet allotted to each soldier, $F$ the number of square feet occupied by each man in the interior,—then

fy = nx, \text{ and } Fy = A, \text{ or } y = \frac{nx}{f} = \frac{A}{F}; \text{ whence } \frac{nFx}{f} = A.

Again, let the perpendicular $Cd$ , from the centre of the polygon (fig. 33) to its side $AB$ , be $p$ ; the distance $db$ from the side $AB$ to the boundary line of the available interior space $mn$ be $d$ ; then $Cb = p - d$ ; and as $Cd : AB :: Cb : mn$ , $p : x :: p - d : mn$ , or

mn = \frac{px - dx}{p} = x - \frac{dx}{p}.

Now, the value of $p$ expressed as a function of $x$ and of the angle of the centre $\phi$ , which is $= x \frac{1}{2} \cot. \frac{1}{2} \phi$ , varies with the nature of the polygon; and replacing, therefore, the variable coefficient $\frac{1}{2} \cot. \frac{1}{2} \phi$ by $\beta$ , $p = \beta x$ , and $mn$ ,

\text{the side of the interior space } mnpo, = x - \frac{dx}{p} = x - \frac{dx}{\beta x} =

x - \frac{d}{\beta}, \text{ and } Cb = mn \times \frac{1}{2} \cot. \frac{1}{2} \phi = \beta \left( x - \frac{d}{\beta} \right). \text{ The}

surface of the interior triangle $Cmn = \frac{1}{2} mn \times Cb$ is therefore

= \frac{1}{2} \beta \left( x - \frac{d}{\beta} \right)^2, \text{ and } A = \frac{n\beta}{2} \left( x - \frac{d}{\beta} \right)^2; \text{ whence}

\frac{nFx}{f} = \frac{n\beta}{2} \left( x - \frac{d}{\beta} \right)^2, \text{ and by reduction } x = \frac{1}{\beta} \left\{ d + \frac{F}{f} + \sqrt{\frac{F}{f} \left( 2d + \frac{F}{f} \right)} \right\}.

The variable $\beta = \frac{1}{2} \cot. \frac{1}{2} \phi$ is as follows:—

In the triangle,	0.288
" square,	0.500
" pentagon,	0.688
" hexagon,	0.866

and taking the square under the following conditions:— $d = 12$ feet, $f = 3$ , $F = 6 \times 3 = 18$ , $x = 62.81$ feet (21 yards), which may therefore be taken as the side of the smallest

square redoubt to be defended by one rank only of soldiers, the garrison being 84 men with a single rank; and a reserve equal to $\frac{1}{2}$ of the garrison; $f = 2$ , and $x = 76.66$ feet, or nearly 26 yards, the garrison being 168 men. If there are

to be two ranks, $f = \frac{3}{2}$ and $x = 89.6 = 30$ yards nearly, the

garrison being 240 men; and if two ranks, with a reserve equal to $\frac{1}{2}$ the whole garrison, $f = 1$ and $x = 115$ feet, or about 38 yards, the garrison being 456 men.

Triangular redoubts are rarely used, from their small interior space as compared with the length of their parapet; thus the smallest triangular redoubt intended to be defended by a garrison of two ranks should have a side ( $x$ ) 54 yards in length, and a garrison of 324, the total length of parapet required to be constructed for this force being 162 yards; whereas a square redoubt of 38 yards' side will accommodate a garrison of 456 men, admitting of a two-rank defence, and of a reserve of $\frac{1}{2}$ the whole garrison, with a total length of parapet of only 152 yards; and this objection of limited space is further strengthened by the great amount of dead-angle space before the salients. Keeping these numbers, as regards square redoubts, in recollection, the engineer will be able at once to determine his arrangement of the proposed garrison, and yet to limit himself to the least amount of work in parapet. If, however, he has to provide for guns, for traverses, or for other constructions, he must increase the side of his square, remembering that in the case of the square of 38 yards' side the augmentation of 1 yard per side will require only the addition of 12 men to the garrison, making it 468, and the additional interior space for their accommodation of 216 square feet; whereas there will be a gain of space of 549 square feet, leaving an excess towards the objects stated of 333 square feet; and if the side were increased to 45 yards, and the garrison to 540 men, there would be a surplus interior space of 2709 square feet, being sufficient for barbettes for three guns and for one howitzer, and for a traverse; and this size may therefore be assumed as the best for a normal redoubt. It is generally stated that, passing this limit, some of the forms of forts should be adopted, as diminishing to a certain degree the defects of redoubts, by introducing more or less perfect flanking defence; but in practice it will be often preferable to use a larger redoubt, as the flanking defence obtained on very short lines must be extremely imperfect, and therefore more liable to deceive by false security than to benefit. In Pl. CCLIX., fig. 5, one of the angles is shown with an indented parapet as a means of correcting the defect of a dead salient; but this is difficult of construction, and it will generally be preferable either to cut it simply off as in another angle of the figure, or to round it as in a third, or to occupy it by a gun en barbette, as in the fourth. Of forts, fig. 6 exhibits a star fort of eight points formed upon a square, which is far preferable to one of six points formed upon a triangle, as giving comparatively more available space. The defect, however, in this trace is, that though the intermediate angle $F$ is sufficiently open—as it exceeds $60^\circ$ ,—the angles $A$ and $B$ are less than $60^\circ$ . Down to the lowest limit of such forts, in which $AB$ of fig. 6 is taken at 60 yards, and the sides $AE$ , $EF$ , $EB$ at 20 yards, there is still sufficient space to accommodate the necessary garrison, which should be in that case about 900 men. It is useless to describe those forms of star forts, which would not accommodate the required garrisons; but that represented in fig. 34 (next page) is well fitted for a large garrison. A simple construction on a pentagon is:—Bisect $AB$ in $C$ ; make the perpendicular $CP = \frac{1}{2} AB$ ; join $AP$ and $BP$ ; make $Bd$ and $Ad$ each $\frac{1}{2}$ of $AB$ , and joins $dc$ , $de$ . In this case the angles at $A$ and $B$ will be $64^\circ$ , and the short sides (with an exterior side of 120 yards) each 23 yards. From what has been already said in a preceding page, half-bastion forts,

Fortification. CCLIX., fig. 12, will rarely be adopted; but when the extent of the proposed garrison is such as to require a large amount of accommodation, and there is time to undertake such works, the bastioned trace should be adopted, as it introduces a principle not observed in the preceding traces, namely, that of defending the whole by a part, the opposite flanks EG, FG of the two bastions GEAFG, GFBFG, defending the intervening curtain GG between them, as well as the faces AE, BF of the bastions—whilst the fire of one flank necessarily sees the scarp of the opposite one and defends it. The bastions are indeed, like their analogous lunettes, works in themselves; the curtain being only a connecting line, forming several bastions into one connected whole. Pl. CCLIX., fig. 7, is a square bastioned fort, but the pentagon is a better form, and should be adopted when practicable. It may be said that the bastioned form of field forts has been derived from the more massive structures adopted in the permanent defences of fortresses, whilst the other traces have naturally sprung out of the earliest and rudest works even of savage tribes, for they too had their redoubts, and have only been reduced to more definite rules by the progress of military science. The history, therefore, of the bastion trace, so interesting in itself, will be postponed to a future page. Little more then requires to be said on this section of the subject, further than to point out the great importance of field-works, in securing a base of operations for an advancing army. Pl. CCLIX., fig. 13, exhibits, for example, a bridge head consisting of a bastioned front, with either simple straight branches or branches provided with a short flank as shown in the figure (see also fig. 35 below). This is, as stated before, technically called a horn work; and if there had been two such fronts so placed as to throw a bastion in the centre, and connected as before with the river by straight branches, the work would have been called a crown work. Lunettes also may be used, and even redans constructed, as fig. 1 of the plate (left side), for a similar purpose, where the object is simply first to secure the bridge from

Fig. 34.

the enemy's attack and fire, and secondly to allow the defending army to manœuvre on the opposite side when desirable: but just in proportion to the numbers passed over

Fig. 35.

the enemy's attack and fire, and secondly to allow the defending army to manœuvre on the opposite side when desirable: but just in proportion to the numbers passed over

Fortification. the bridge, and to the extent of advance contemplated, will it be necessary to increase the importance of the works forming the bridge head, as it will be often necessary to form more than one bridge in connection with it. Nothing can be more fatal to a retreating army than to find itself driven back to a river, and to have no sufficient line of intrenchment to enable it to maintain its ground whilst its arrangements for passing the river are in progress. Fig. 35 exhibits one such arrangement in which the horn work front has been much enlarged, and a lunette as a keep introduced within it. The mode in which the troops can move out at the sides, under protection of covering and flanking parapets, is shown, as well as the barbettes for guns, which become necessary in works having so important an object. Fig. 36 represents a line of tenaille intrenchments in front

Fig. 36.

of the lunette, and a line of intrenchment is also shown on the near side of the river, from part of which the last terminal branches of the tenailles are flanked. In this figure T, T represent traverses, and F, F either chains or lines of pickets placed across the stream; the object of the first being to secure the bridge from the ricochet fire of the enemy, and of the second to secure it from destruction by burning or explosive bodies launched by the enemy in the stream, and allowed to float down. More extended intrenchments might be formed of lines of lunettes with intervening intrenchments; but it is unnecessary to pursue the subject in this suggestive manner further, as the engineer must necessarily adapt his works to the nature of the ground, and to the extent of the army for which he is required to prepare in this manner a defensive position, from which it may either advance or retire, without risk or confusion, as the necessities of war may require.

RAMPART OR TOWN FORTIFICATION.

If, as has been stated, the simple lines or works of para-Rampart pet fortification appear to have been adopted even by the fortification. rudest tribes of wandering savages, for their temporary defence or security, the more massive and artistic works of rampart defence would seem to imply a certain amount of civilization. As an art, indeed, fortification is very nearly as ancient as the existence of society. When men first assembled together for the purpose of mutual protection, and placed their habitations on the same spot, the law of necessity, springing in this case out of the principle of self-defence, rendered it indispensable for them to adopt some means for securing their families and their property against the sudden inroads of enemies. Hence, when Cain, the son of Adam, built a city, he surrounded it with a wall; and, in like manner, the Babylonians, when they built cities soon after the Deluge, encompassed them with similar defences. In the early ages, men considered themselves as sufficiently protected by a single wall, from behind which they could with safety discharge their darts, arrows, and other missiles, against an assailant. But when, in the progress of improvement, new and more powerful means of attack were discovered, it became necessary to increase, in a corresponding degree, the inert force of resistance; and

accordingly the feeble defensive structures of the primitive ages were in time succeeded by solid ramparts, flanked and commanded by elevated towers. In short, as the power of attacking fortresses or places of strength was augmented by successive devices and inventions, the means of resistance were proportionally increased, until the art of fortification arrived at a state of comparative perfection, in which it remained for many ages nearly stationary.

The various improvements which were from time to time made in strengthening the walls, and adding to the defences of ancient cities, are recorded in history, and need not be detailed in this place. The first walls which we read of consisted of brick, the material employed by Cain for the protection of the city which he founded, and called by the name of his son Enoch. Amongst the ancient Greeks, brick and rubble stones intermixed were used for the same purpose, as we find from the description of the wall which connected Mount Hymettus with the city of Athens; but, in addition to such structures, should be noticed the works, surrounding several cities, of Cyclopean structure, built of huge stones, placed with their longer axis transversely to the line of wall, and arranged with great care and skill, though without mortar. The walls of Babylon and Nineveh indicate a prodigious advancement in the art of fortification, and are justly accounted amongst the wonders of the ancient world. Those of the former city, ascribed by some to Belus, and by others to Semiramis, were thirty-two feet in thickness, and one hundred feet in height, surmounted by towers at an average ten feet higher, and cemented by means of bitumen or asphaltum; they encompassed a vast area, and presented a solid defence, which no means of attack known in ancient times were sufficient to overcome or beat down. The walls of Jerusalem, though of smaller dimensions, appear to have been little inferior in strength and solidity to those of Babylon; for, in the siege of that capital by Vespasian, all the Roman battering-rams and other engines, though used with the utmost vigour, required a whole night to disengage four stones in the masonry of the tower of Antonia. But when fortification had arrived at the state in which we find it in the works of these and other cities, it remained stationary for ages, and perhaps even retrograded somewhat, until the discovery of gunpowder, the invention of artillery, and the application of both to military purposes, effected an entire revolution in the principles of attack and defence. Then the round and square towers, which had formed secure flanking defences against assailants armed only with arrows and with darts, afforded no protection against the projectiles discharged by cannon; and even those battlements which had defied the catapult and the battering-ram speedily yielded to the force with which they were now assailed, whilst their defenders were at the same time destroyed, or buried in their ruins.

It being thus found that the ancient system of fortification was of little or no avail against the new method of attack which had been discovered, and which came into general use towards the close of the fifteenth century, it became indispensably necessary to adopt another method of defence. The plan of fortifying with bastions is believed to have commenced with the Italians early in the fifteenth century: though Papacino D'Antoni, professor of artillery and engineering of Turin, states, in his Architettura Militare (1759), that several small bastions had been constructed in the preceding century, and that the ruin of a large bastion which had formed part of the fortifications of Turin, built for Duke Louis of Savoy, still existed in the royal gardens at that time. The bastions on the enceinte of Verona, built by the Italian engineer Micheli, in the year 1523, are generally supposed to be the oldest extant; and the next, probably, are those still to be seen in the citadel of Antwerp, and which were constructed for the

Emperor Charles V. in the year 1545, by the Italian Fortifica-
engineer Paciotto D'Urbino. These bastions are small, tion.
with narrow gorges and short flanks and faces; and they are placed at a great distance from one another, it being the invariable practice, at the time when they were built, and for a considerable time afterwards, to attack the curtains, and not the faces, of the bastions.

Errard of Bois-le-duc, one of the principal officers of the engineer corps first organized by Sully, prime minister of Henri IV., and from which has sprung the French Corps du Genie, was the first in France who laid down rules respecting the best method of fortifying a place, so as to cover its flank. At the command of the minister, he wrote a book on the subject, which was published in 1594, and in which the details of his method are explained. As a writer on fortification, he was preceded in France by Beril de la Treille, who published his work on fortifying towns and castles in 1557. Errard fortified inwards; and in the square, pentagon, hexagon, heptagon, and octagon, he made the flank perpendicular to the face of the bastion; but in the enneagon, and in all polygons of a greater number of sides, he made it perpendicular to the curtain. In endeavouring to accomplish his object, however, he made the gorges too small, the embrasures too oblique, and left the ditch almost defenceless. This engineer constructed part of the enceinte of the citadel of Dautens, as well as the citadel of Amiens, and also some works at Montreuil and Calais.

The Chevalier Antoine de Ville, who succeeded Errard, published a treatise, dated 1629, in which he completed much that his predecessor had only sketched, and rectified various defects in the method of the latter. The Chevalier was employed under Louis XIII., and constructed new enceintes for Montreuil and Calais. His plan of fortifying has been denominated by some the French method, and by others the Compound System (Système à trait composé), because it united the Italian and Spanish methods, from the latter of which it differs only in having no second flanks and fictitious lines of defence, and in not confining the flanked or salient angle of the bastion to ninety degrees. The leading maxims of the Chevalier de Ville were, to place the flanks perpendicularly to the curtain, to make them equal to the demigorges, or each equal to a sixth part of the side of the interior polygon, and, in the hexagon and all higher polygons, to confine the flanked angle to ninety degrees. But this plan is liable to nearly the same objections as that of Errard; for here, also, the embrasures are too oblique, especially in the polygons, and the ditch is necessarily but ill defended.

Sixteen years after the publication of De Ville's treatise appeared the work of the Comte de Pagan, which issued from the press in 1645, and contained the development of a system which, in a short time, entirely superseded those of his predecessors. In fact, it was the Comte de Pagan who first disengaged the science of fortification from a number of suppositions which custom had in some measure consecrated, and which, resting more on abstract mathematical reasoning than on practical observation and experience, had hitherto retarded the progress of the art. This engineer acquired great reputation during several sieges which he assisted in conducting under Louis XIII.; but having become blind at the age of thirty-eight, he was obliged to retire from the service, in which he had already obtained the rank of maréchal-de-camp, and he died six years after completing the treatise above-mentioned, in which he embodied a full exposition of his system. The Comte de Pagan made the flank perpendicular to the line of defence, in order as much as possible to cover the face of the opposite bastion; and he also pointed out a method of building casemates in a manner peculiar to himself. Vauban borrowed from the Comte de Pagan the length of his perpendicular, and Allain Manesson Mallet, whose construction

Fortification. still remains in favour with many, also proceeded upon the principles laid down by this scientific soldier.¹

The Maréchal de Vauban was born in 1633; and in 1655, at the time of the Comte de Pagan's death, he had already acquired reputation at several sieges. Vauban followed up the principles suggested by Pagan, and employed them extensively in practice, with consummate skill and judgment. He constructed thirty-three new fortresses, repaired and improved one hundred; and having conducted about fifty sieges, he left his extensive works, and a treatise De l'Attaque et de la Défense des Places, published in 1737, to speak for themselves. From the different constructions observable in these works have been compiled the systems which, in the military schools, are denominated Vauban's first, second, and third systems of fortification, and which the reader will find developed in the sequel. Had the genius of Vauban been applied to the discovery of a method for securing a permanent superiority to the defence of fortified places, posterity would have been greatly indebted to him, and even humanity would have had cause to rejoice in such a triumph of military art. But, being engaged in the service of the most ambitious monarch of modern times, Louis XIV., he applied his great talents to forward his master's views, and soon perfected that irresistible system of attack,² which has ever since been so successfully followed. Before his time the general superiority was on the side of the defence; but ever since, the case has been so completely reversed, that the success of an attack made with adequate means, and scientifically conducted, is a matter of ultimate certainty.

Nor should the protracted siege of Sebastopol be considered an exception to this rule, as the principal cause of its hitherto successful defence must be sought in its freedom from investment and the consequent incessant renewal of its garrison, thus withdrawing the siege operations from the influence of the sound maxims of Vauban.

Considering that at this time, when the public mind is generally impressed with a desire to have a more practical bearing given to general education, there still may be a tendency on the part of public authorities to retrograde as regards military education, and to substitute for the mathematical sciences the classical languages, it is well to notice briefly the characters of Errard, of Pagan, and of Vauban. Errard was one of the most distinguished members of a corps formed out of the best instructed and most experienced military men he could find, by the great Sully, who was grand-master or master-general of the artillery in the reign of Henri IV. of France. This corps, called by Sully "Engineers in ordinary to the King," has now become the Corps du Génie, and has to this day maintained its high character as a body of scientific men. Comte Pagan had from his earliest years devoted himself to the study of mathematics and fortification. At the age of thirty-eight he was afflicted by blindness, but before that time he had served with distinction at twenty-five sieges, and acquired the rank (then second only to that of marshal of France) of field marshal. Besides his celebrated work on fortification, he published several others on Astronomy. Vauban was no ordinary man in any sense. As the inventor of parallels in sieges, and of the ricochet fire, he stands on the first rank of military engineers for invention, and when it is considered that he conducted fifty-three sieges and shared in 140 battles and skirmishes, he must be considered an equally experienced one. At fifty-five years of age he attained the highest honour of the French army, being created marshal of France; yet amidst this stirring and successful military life he never failed to

Fortification. turn to account the geometrical knowledge for which he was distinguished when a youth, and which had obtained for him the early notice of the Prince de Condé. His mind was, therefore, never idle, but constantly directed to projects of public utility, whether military or civil, and he left behind him records of such labours in twelve folio manuscript volumes, entitled Mes Oeuvres, at once a monument of his own ability and industry, and a beacon to guide subsequent engineers to that course of useful as well as intellectual activity which it ought to be their pride to follow.

M. Minno Baron de Coehorn, first a general of artillery, then a lieutenant-general of infantry, and ultimately director-general of all the fortified places belonging to the United Provinces of Holland, was the contemporary and rival of Vauban. This able engineer, convinced that, however expensively the rampart of a town may be constructed, it cannot long resist the shock of heavy ordnance, invented three different systems for throwing such obstacles in the way of a besieging force, that, although the place be not thereby rendered impregnable, it can only be approached with great difficulty and hazard. But these methods, without much modification, are only applicable to low and swampy situations, such as are to be found in Holland, and are therefore not available where the localities are of a different or opposite description. At the same time, Bergen-op-Zoom, Mannheim, and other places fortified by this engineer, particularly the two former, have very great merit, inasmuch as it is impossible for a besieger to penetrate into any of the works, without being exposed, on all sides, to the fire of the besieged, who are under cover; and from artillery and musketry it is scarcely possible for an assailant to shelter himself. In fact, Coehorn was a great master, and combined, as will be observed hereafter, many of the means of defence springing from another source with the bastioned trace. He published his first work on fortification before he had acquired much practical experience; and in fortifying Bergen-op-Zoom, which is allowed to be his masterpiece, did not reproduce, except as fragments, any of his published systems.

Since Vauban's time several improvements have been suggested, particularly by Cormontaigne, who entered the corps of French engineers in 1716, nine years after Vauban's death, and died a maréchal-de-camp in 1750. Some account of the system of Cormontaigne will be found in a subsequent part of this article. The three methods delivered by Belidor are all applicable to an octagon of two hundred toises. Scheiter distinguished his systems into great, mean, and little, in imitation of Pagan, requiring the exterior sides of the polygon to be, respectively, two hundred, a hundred and eighty, and a hundred and sixty toises: he adopted from Castriotto detached bastions, and made use of a continuous fausse-braye. Fritach, a Pole, proposed two methods, which he exemplified on different polygons. Dogen, a Dutchman, published a large volume on fortification, in which, after enumerating various modes employed by different writers for determining the salient angle, he selected three as the most approved, and proposed as many methods of construction, one of which is borrowed from Fritach, the Pole. Pietro Sardi, an Italian, suggested a peculiar method of construction on a hexagon. The Sieur de Fontaine found the flanked or salient angle of the bastion by adding fifteen degrees to half the angle of the figure, from the square up to the dodecagon, in which last it becomes ninety degrees, and at this he continued it in all the higher polygons. He also constructed outwards, and, in every regular figure, made the curtain equal to seventy-two

¹ Mallet constructs outwards, making in every figure or polygon the demigorge equal to a fifth part of the side of the interior polygon or figure, the capital of the bastion equal to a third part of the same side, the curtain equal to three-fifths or thrice the demigorge, and the angle of the flank equal to 98°. The faces of the bastions and the flanks are determined by the lines of defence, which are razant. From these data all the other lines and angles are easily found.

² See his work De l'Attaque et de la Défense des Places, passim.

toises, the face of the bastion to forty-eight, and the flank, which he placed perpendicularly to the curtain, to eighteen toises, or a fourth part of the curtain. Ozanam and Muller delivered each four methods of construction, the particulars of which will be found in their respective works. In 1751, Charles Bisset, who, as an engineer-extraordinary, served with the Duke of Cumberland in the Netherlands, and was present during the siege of Bergen-op-Zoom by the Maréchal Lowendahl, published a treatise on the theory and construction of fortification, in which there are many sensible and judicious remarks; and the same general description may be applied to an Essai sur la Fortification, ou Examen des Causes de la grand supériorité de l'Attaque sur la Défense, published anonymously in 1755. In a work entitled Science de la Guerre, which appeared at Turin eight years before the date last mentioned, a new method of construction is proposed, in which the principal objects to be attended to are, that there be mines under all the works, and that a regular communication be kept up with the chambers by means of subterraneous galleries, to be resorted to in proportion as the enemy approaches the body of the place. The third volume of the Œuvres Militaires contains some useful observations and maxims relative to irregular fortification; and in the Supplement to the Récrées of Mareschal Saxe, by Baron d'Espagnac, the subject of fortification generally is amply discussed, and an accurate description given of the different means of attack and defence. Besides the writers above enumerated, may be mentioned the Chevalier St Julien, an able engineer, who published a method by which, he asserts, works may be constructed at a less expense, yet in such a manner as to render the defence or attack more formidable; Francisco Marchi, of Bologna, who, in 1599, furnished no less than a hundred and thirty-nine different methods of constructing fortifications, many of which are very valuable, and afforded useful hints to subsequent engineers, who have indeed greatly profited from his work; Bombelle, who established three kinds of fortification, called the grand royal (grand royal), the mean royal (moyen royal), and the little royal (petit royal); Blondel, who published a system divided into two principal heads, the great and the little, whose exterior sides are respectively two hundred and a hundred and seventy toises; Donato Rosetti, a canon of Livorno, who wrote on the method of constructing works in what he calls fortification à rebours, or fortification in reverse, so denominated because the re-entering angle of the counterscarp being opposite to the flanked angle, it will, according to him, be necessary to attack it from the reverse side of the other works; and Antonio de Herbart, major of artillery in the Duke of Wurtemberg's service, who published a treatise on fortifications with what he calls angular polygons. The treatise entitled Nouvelle Manière de fortifier les Places, tirée des méthodes du Chevalier de Ville, du Comte de Pagan, et de M. Vauban, avec des Remarques sur l'ordre renforcé, sur les desseins du Capitaine Marchi, et sur ceux de M. Blondel, which appeared in 1689, is full of strong reasoning, whence the author deduced a new system; but it contains little that is really original, though it gives numerous references to what had previously appeared, and disposes the different parts in a judicious manner. M. de Montalembert's system of casemated and reverse fire has been in part adopted in the splendid fortress of Alessandria in Italy, constructed under the directions of Napoleon.

Of the more recent treatises on fortification, by far the most elaborate and complete is that of M. de Bousmard, entitled Essai Général de Fortification, d'Attaque et de Défense des Places, dans lequel ces deux Sciences sont expliquées et mises l'une par l'autre à la portée de tout le monde; a work which enjoys a deservedly high reputation.

It is remarkable for great accuracy and research, and may be considered as embodying in itself every thing that is valuable in connection with the subject of which it treats. M. de Bousmard's work, therefore, though intended to serve as an elementary treatise on fortification, is too expensive for the pecuniary means of a great number of inferior officers, whose instruction the author professes to have had chiefly in view: but to teachers of fortification it is altogether indispensable; and as long as the science and practice shall continue on their present footing, it will be deservedly considered as the most comprehensive and valuable work on the attack and defence, as well as the construction, of all kinds of fortification.

With regard to Carnot's Traité de la Défense des Places Fortes, it was written to serve a temporary purpose; and the exaggerated celebrity which it acquired on its first appearance has been succeeded by an equally unfounded neglect. The more prominent innovations recommended in this treatise were, first, an alteration, which, however, was not original, in the trace or outline of the polygon; secondly, the suppression of the exterior revêtement of the covered-way, known as the counterscarp; thirdly, the detachment of the scarp-wall from the rampart, and the construction of the latter without revêtement; fourthly, destructive personal conflict with the besiegers by means of frequent sorties; and, lastly, making vertical fire the basis rather than an accessory of the defence. With regard to the first of these proposals, all of which the reader will find very ably discussed in Jones's Journals of Sieges in Spain and Portugal,¹ we have only to remark, that by means of an increased expenditure for retrenchments and casemates, as recommended by Carnot, the strength of particular portions of the polygon may be increased; and that, if he has failed in tracing a perfect front, founded on the basis of Montalembert's system of casemated and reverse fire, he has at least rescued a valuable suggestion from unmerited neglect, and rendered an important service to science by directing the attention of military men to the means most likely to create a barrier against the growing powers of the attack.

The Traité de Fortification Souveraine, suivi de quatre Mémoires sur les Mines, by M. Mouzé, lieutenant colonel of engineers in the French service, was published at Paris in 1804, and is justly considered as the most complete work on the subject it treats of which has yet been given to the public. Subterranean fortification is a branch of the art which, until a very recent period, was wholly neglected in this country, and in which our engineers were far behind their brethren of the continent. We learn from Colonel Jones's work on the Peninsular Sieges, that the Duke of Wellington's army in Spain was unattended by a single regularly-trained sapper or miner until late in the year 1813; and many valuable lives were sacrificed, from the want of these valuable, or rather indispensable auxiliaries. In this respect things are now changed, and the engineer has the assistance of a body of men well instructed in the duties of the trench, the sap, and the mine; but it cannot yet be said that the corps of sappers and miners has been sufficiently augmented, whilst it may be feared that the growing idea that the ordinary navvies might with advantage replace them, may check the desire of increasing the body. In war, it must be remembered that discipline is as important as skill, and that the labourer who would have worked with the greatest effort under ordinary circumstances might be found very ineffective when forced to work on his knees in a sap, and when exposed to an enemy's fire obliged to remove calmly the man before him when killed, and then, with equal composure, to step into his place.

The preceding hasty and imperfect summary of the pro-

Fortification. progress and literature of fortification has been given principally in connection with the bastioned trace, as the one more generally used both in the French and English schools in teaching the principles of the science; and justly so, as, theoretically speaking, it exhibits the most perfect arrangement of flanking or reciprocal defence. It is, however, desirable, before going further, to recur back to the earlier epochs, and to investigate the manner in which the ancient arrangement of a wall, with its round or square towers, passed into the present systems of defence. The accompanying figure (No. 37), will explain the natural and pro-

Figure 37: A technical diagram of a fortification system. It shows three main structures: a square tower-fort (B) on the left, a pentagonal bastion (A) in the center, and a circular tower-fort (C) on the right. These are connected by a series of walls and lines representing the lines of defence. The diagram includes various labels: 'a' and 'c' for angles at the square tower; 'b' and 'd' for angles at the pentagonal bastion; 'm' and 'n' for the connecting walls; 'de' and 'fa' for the flanks of the bastion; 'cb' and 'ab' for the faces of the bastion; and 'nn' for the flanks of the circular tower. The diagram illustrates how the old tower-fort was changed into a pentagonal bastion and how the connecting walls were modified.

Fig. 37.

bable manner in which the old tower or rather tower-fort (baluardo) was changed into a pentagonal bastion. If, for example, lines of defence be drawn from the extremes of two adjacent curtains to the angles a and c of the square tower-fort A, a space would be left, c a b, unseen from the adjacent forts B and C, and therefore undefended, except by downward or vertical fire from machicolis, or projections from the walls supported by corbels made for that express purpose. Such a space would be turned to account by the besiegers in fixing their scaling ladders; and the change of the straight line ac into the two faces cb, ab seems but the result of a self-evident necessity. As the work became enlarged, the portions of the fort within the connecting walls m m were omitted, and the flanks de, fa alone remained of the old work, forming with the faces the bastion faced, which only required to be improved in proportions to become the bastion of modern times. It is, however, said that the towers were sometimes placed with an angle salient as in B, and if so, omitting the portions n n, the resulting bastion has a strong analogy to those of Errard before mentioned. By using the old wall merely as a retaining wall, and as an obstacle against escalade, and adding to it a rampart and a parapet of earth, the Italians completed the system of bastioned defence, which, notwithstanding all the modifications of the French, ought to be called the Italian system. In this system, whilst imitating the construction of the old towers by using casemated or masonry-vaulted chambers for artillery, in addition to the guns mounted on the rampart, the Italians placed the musketeers on the banquette of the parapet, and made them fire over it. Now this arrangement of the musketry fire is an essential characteristic of the Italian system, and the relief of the several works are hence restricted within certain limits, as it is necessary so to determine the levels of the opposite flanks that the fire along their superior slopes shall defend the whole of the intervening curtain: but there are other modes of using musketry as well as artillery fire in the defence of the ditches, and on these were founded other systems of fortification.

The first Italian writer on fortification was Tartaglia, whose work was published in 1546; but the really first writer on the science was Albrecht Dürer, at once a great painter, a sculptor, an engraver, and a civil and military architect, whose work is dated 1527, being published one year before his death. This remarkable man founded his system on the old circular tower-forts C, fig. 37, in which the dead space is much less than in the square, and enlarging them to an enormous extent, he adopted the word, "Bastei," or in

the plural "Basteien," for his new work. As the attention of military men was at this early period more directed to cannon than to the rude musket as an instrument of defence, it was natural that the latter should be less considered in these arrangements than the former. Dürer based his systems on the principle that the defences of basteien or other works which depend only on the cannon placed on their terreplein, may be effective whilst the enemy is at a distance, but cannot be so when the enemy, under cover of his epaulements, has advanced to the ditch; and leaving therefore to the cannon on the terreplein the task of firing upon the enemy's troops and batteries at a distance, he placed his cannon, and it may be said also his musketry, either in vaulted galleries running along the base of the scarp, or in caponnières, also vaulted or casemated works, built across or transverse to the ditch. The great circular bastei of his third and most improved system was no less than 130 yards in diameter, with a scarp 120 feet high, a ditch in

front 100 feet wide, and a massive envelope, about 80 feet thick and 100 feet high, formed of earth with thick masonry revêtements both in front and in rear, as a mask between the main work and the counterscarp. Such gigantic proportions as these have led many to consider Dürer as little more than a speculative writer, but this would be an unjust estimate of his real merits. Reducing his works to more reasonable dimensions, they would, with proper modifications, have become practicable, and have afforded many useful hints to the scientific engineer. The defects of the circular form were compensated by the grazing fire of the caponnières in his system, and the main work was retained in an effective state by the cover afforded to it by the envelope. We shall have occasion to refer again to Dürer, but in the meantime it may be said that whilst the Italians are properly considered the originators of bastioned systems with an earthen parapet over which the musketry fire is directed, Dürer has an undoubted claim to be considered the author of the other branch of fortification in which casemated defence in the main works, as also in caponnières, becomes the essential characteristic—a branch which has proved as fertile in results in modern times as the bastioned system.

SYSTEMS OF PERMANENT FORTIFICATION.

1. Vauban's First System.

Before commencing to draw a plan of fortification, it is usual to determine upon some polygon on which to describe it. In this figure, accordingly (see Plate CCLX. fig. 1), we have taken the angle of an octagon, and called the length of the side 360 yards. In constructing a fortification, a figure is determined on, as near that of a regular polygon as possible, within which the enceinte or chain of main works is to be contained. The enceinte or body of the place consists of as many bastions, connected with curtains, as there are sides to the figure, and each of these is made as near 360 yards as possible, so that every part may be within range of such arms as are to be employed in its defence.

The principal or outline denotes the contour or line by which the first figure of the work is defined. This line is supposed to pass along the superior part of the cordon, and is that from which all the other parts of the work are set off.

The exterior side, or side of the polygon above mentioned as equal to 360 yards, is that upon which the front of the fortification is described, and it extends from the flanked angle of one bastion to the corresponding angle of the next, as AB. These lines are bisected, and a perpendicular, DC

Fortification. is drawn from the point of bisection towards the place, its length being proportional to the extent of the exterior side and adjacent angle of the polygon; that is, one-sixth for the hexagon and all figures of a greater number of sides, one-seventh for the pentagon, and one-eighth for the square.

The lines of defence AEG, BEH, are drawn from the extremities of the exterior sides through these points, and produced to an indefinite length; and upon the lines so drawn are set off two-sevenths of the exterior sides, equal to 1024 yards, which marks out the point for the shoulder of the bastion E and F. The distance between these points is then laid along the continuation of each line of defence, and a line is drawn connecting them the curtain GH, from the extremities of which lines are drawn to the point marked off for the shoulder of the bastion, and thus form the flanks. And in this manner is drawn a front of fortification, which being repeated round the sides of the polygon, completes the works of the enceinte or body of the place.

Vauban divided his first system into three parts; namely, the little, the mean or intermediate, and the great. The first he used for small forts of four or five sides, citadels, horn-works, and crown-works, making the exterior sides from 120 to 240 yards, the perpendicular in the square equal to one-eighth, and in the pentagon one-seventh, and the faces of the bastions in each equal to two-sevenths of the exterior side. In the mean or intermediate, which is adapted for all sizes of towns, the exterior side varies from 250 to 360 yards, the perpendicular is one-sixth, and the faces are two-sevenths. In the great the exterior side varies from 360 to 520 yards. This kind was never adopted for all the sides of a place, but only when one of these happened to be near a river or a marsh; in which case the distances of the bastions should be so regulated that they may not be out of musketry range from one another. When the curtain becomes unavoidably too long, this defect is in part remedied by erecting on it a flat bastion, which is not so high as the rest of the works.

Ground which will admit of being regularly fortified throughout is seldom or never to be met with, but, nevertheless, the rules of regular fortification must be observed as nearly as possible; that is, the flanked angles should not be less than 60°, the lines of defence should not exceed musket range, and the sides should be lengthened or shortened so as to obtain a well-proportioned front upon each. After an irregular place has been reduced to as regular a form as possible, lines are drawn parallel at the distance of about 30 yards from the houses, in order to give sufficient space for the rampart; and these lines form the interior polygon, which may be fortified inwards, by setting off the demigorges of the bastions, and raising their flanks at an angle of 100° with the curtain. Or, the exterior side may be formed and fortified inwards by drawing a line parallel to each of the interior sides; and when the angle is that of a polygon of more than five sides, the distance from the exterior to the interior sides should not be less than 100 yards. If a side extend from 360 to 520 yards, the perpendicular should be diminished to about 50 yards, and the faces of the bastions be made from 100 to 120 yards. When a side is very long, it may be divided into several parts of from 340 to 360 yards each, which may be fortified with flat bastions, as was occasionally done by the Italians, an example of which may be seen in the bastion Anastasius at Corfu. All these dimensions may, however, be now much increased, and placed more in relation to the range of the modern musket.

The ditch or fosse is an excavation of from 12 to 24 feet in depth, and from 30 to 50 yards in breadth, surrounding the rampart on the exterior side, and the earth dug out of which serves to raise the rampart and parapet. The side of the ditch next the place forms part of the escarpe, the side

next the country is called the counterscarp, and it is made circular opposite the salient angles of the works. In fig. 1 arcs are described with a radius of 30 yards, opposite the salient angles of the bastions, tangents to which are drawn upon the shoulders of the neighbouring bastions, and thus form the ditch. The general dimensions of a ditch should be such that its excavation, or deblai, would produce sufficient earth, or remblai, for the formation of the works. The breadth varies from 30 to 50 yards, in order that, in passing across it to the assault, the enemy may, for a considerable time, be exposed to the fire of the works; and its depth must also be such as to render difficult the escalade of the parapet, as well as to prevent the besiegers at the crest of the glacis from being able to see to breach the lower part of the revêtement of the escarpe. The line of the counterscarp is drawn from the rounding at the salient angles of the bastions upon the shoulders of the bastions next adjoining, in order that the whole of the ditch may be defended by the fire of the flanks of the collateral bastions. Ditches are of three kinds; wet, dry, and such as may occasionally be rendered either wet or dry. The wet ditch is calculated to prevent sudden surprises or assaults, excepting during hard frost, as in the attempt made to surprise Bergen-op-Zoom in the year 1814; but, independently of this exception, the number of bridges of communication, which require continual repair, and the difficulty of making sorties, which a wet ditch creates, renders it extremely inconvenient. A dry ditch, which is capable of containing works for its own defence, and by means of which communications round the works may more easily be maintained, is therefore preferable to a wet one; but the third kind, which unites the advantages of the other two, should, when practicable, be preferred to either. It is only in particular situations, however, that the advantage of such a ditch can be obtained.

The tenaille, in the form given to it by Vauban, does not appear in the works of earlier engineers, but it seems to be naturally derived from the trace of Rimpler (1673), in which the middle flank is analogous in function to the tenaille, and occupies its position; it is a work placed in front of the curtain, and is formed by the continuation of the lines of defence, at the distance of ten yards from the angle of the shoulder; the ends are then drawn parallel to the flanks of the bastions; it is made sixteen feet broad; the angle formed by the meeting of the two lines which determine its rear is then cut off, at the distance of ten yards, parallel to the curtain; and another line is drawn at the distance of sixteen yards, parallel to this, and forming a small curtain upon the line of defence or front of the tenaille. The relief or height of the tenaille is determined by that of the neighbouring flanks, and it has a parapet of seven or eight and a half feet in height, and from twelve to fifteen feet in thickness. The use of the tenaille is to cover the postern gate, which is often made in the curtain or flank, when the ditch is dry, to protect the troops who may be formed behind the work for the defence of the ditch; and when the ditch is a wet one, to cover the boats which may be collected for the same purpose. It also serves to augment the defence, as its fire, from being more horizontal, and nearer to the plane of the bottom of the ditch than that from the flanks, is of course proportionally more effectual.

The ravelin or demilune was a work originally designed to cover the entrance gate and ridge of a fortress, but it soon assumed the dimensions and performed the office of a most important work of defence, appearing as such in some early Italian traces. Speckle, the great German engineer, who fortified Schlottstadz, Hagenau, Ulm, Colmar, Bâle, and Strasbourg, was, however, the first who recognized fully its importance, and laid down as a rule that "great ravelins materially augment the defensive power of

Fortification. a bastioned system." Acting upon this principle, the ravelins of Speckle were even larger than are those of Cormontaigne's system, and covered nearly the whole of the faces of the bastions, the faces of the ravelin being directed on the salients of the bastions and their capitals, extending about 150 yards in advance of the exterior side of the polygon. Speckle was another man of science, having studied mathematics and military engineering in his youth, and then perfected his knowledge by personally visiting and studying the most remarkable Italian fortifications existing in his time. The Ravelin is a work constructed opposite the curtain, and composed of two faces meeting in an outward or salient angle, with two demi-gorges formed by the counterscarp. Its use is to cover the curtain, the gates, and the flanks of the bastion. The ravelin is constructed as follows: eleven yards are set off along the faces of the bastion from the shoulder; an arc is described from the angle of the flank upon the perpendicular produced, with a radius of 160 yards; from this intersection lines are drawn bearing upon the points set off at eleven yards from the shoulders of the bastion, but not further than the lines of the counterscarp; and at the intersection of the lines of the counterscarp or re-entering angle six yards are set off on the capital or line bisecting its angle, whence lines are drawn parallel to the lines of defence till they meet those of the counterscarp. Stairs, called pas-de-souris, are constructed here in order to facilitate the entrance of the ravelin from the ditch. The ditch in the ravelin, which is twenty-four yards in breadth, is made circular at the salient angle, and drawn parallel to the faces till it joins the main ditch.

The covered-way was first described by Tartaglia in 1554, so that it must have been used at a very early epoch of Italian fortification. Some of the first bastioned fortresses were, however, without this highly important work; and it is recorded that at the siege of Vienna by the Turks, the garrison having made a sortie, some companies were pursued by the Turks up to the counterscarp, and forced over it into the ditch. The necessity of being able to assemble the troops intended for a sortie under cover from the enemy's fire, and to afford them when repulsed a place for reforming and checking the enemy's progress, and thus insuring an orderly retreat into the body of the place, soon became apparent, and a covered-way was supplied to works originally constructed without one. It is a space of ten yards in breadth, extending all round the counterscarp of the ditch, and covered by a parapet of from seven to nine feet in height, with a banquette. The superior part of this parapet forms a gentle slope towards the country, which terminates at the distance of from forty to seventy yards; and this slope is called the glacis. The covered-way serves for drawing up troops in order to make sorties, and costs less than any other part of the works in proportion to the difficulty of taking it. In the salient and re-entering angles of the covered-way spaces are contrived which have been denominated places of arms.

The salient places of arms are formed by the circular parts of the counterscarp, and the prolongation of the branches of the covered-way till they intersect. The re-entering places of arms are constructed with two faces, forming a salient angle of $100^\circ$ with the covered-way. The demi-gorges of the re-entering places of arms are generally from twenty-four to thirty yards; but when they are intended to contain a redoubt or intrenchment, they are from forty to forty-eight yards. The re-entering places of arms are meant to flank the branches of the covered-way, and to contain the troops for its defence. The salient places of arms also serve for assembling the troops destined to defend the covered-way.

Traverses are constructed across the covered-way, upon the prolongation of the sides of the ravelins and bastions,

perpendicular to the line of the counterscarp; they are from eighteen to twenty feet thick, and serve to cover the troops from the enfilading fire of the enemy. Other traverses should be constructed between these, so that the distance from the one to the other should not exceed thirty-six or forty yards. Openings are cut into the parapet of the covered-way about ten or twelve feet wide, in order to keep up the communication from one part to another round the ends of the traverses, which, however, may be shut by a gate when required. In the more improved systems of Cormontaigne and others, these passages are constructed in such a manner that each can be defended by the fire from the traverse in rear of it.

The glacis, as already stated, forms a gentle slope or declivity from the parapet of the covered-way towards the country, and varies from forty to sixty yards. Its parapet cannot be ruined by the fire of the enemy; it covers the revêtement of the body of the place; and being an inclined plane, it can be easily seen and defended from any part of the works.

The rampart is an elevation of earth, being the part of the works situated next to the town. It must be thick enough to receive a mound of earth, called the parapet, and also leave sufficient space behind it for working the guns, as well as room for the defenders to pass round freely. The ditch is immediately in front of the rampart, the faces of which are revêted or built up with stone walls, backed interiorly, at every fifteen or twenty feet, by buttresses or counterforts of masonry, to strengthen it. The rampart is divided into the interior slope, the terreplein, the banquette, the parapet, and the exterior slope or escarpe. See fig. 4, profile.

The revêtement or face of masonry around the work on both sides of the ditch is intended to prevent the earth forming the rampart from falling into the ditch. To ascertain the proper thickness of masonry for this purpose has always been a work of considerable trouble and difficulty. General Sir Charles Pasley of the royal engineers has given the following rules: 1st, For full-scarped revêtements without berms, and for demi-revêtements having berms equal to one-fourth the height of the masonry, the thickness of the wall should be seventeen-sixtieths, and the length of the counterforts or buttresses one-fifth of their height. 2dly, For demi-revêtements without berms, the mean thickness of the wall should be three-tenths, and the length of the counterfort one-fifth of the height. 3dly, For counterscarp revêtements, having only to retain simple terrepleins, the mean thickness should be one-fourth, and the counterfort one-sixth of the height. In all these cases Colonel Pasley supposes the revêtement to be countersloped, that is, to have the exterior slope in a vertical plane, and the interior face inclined, so that the base of the wall may be broader than its upper surface by one-fifth of its height; and he also supposes the counterforts to be rectangular, and the intervals between their centres to be equal to four times their width. 4thly, He recommends that the foundations be made deeper in rear than in front, and that the courses of masonry form an angle with the horizon of about $10^\circ$ excepting at the exterior points, where it should be made horizontal, to prevent the rain from penetrating, and that the interior face of the wall should be of an irregular form. In order to diminish the lateral pressure of the earth against the revêtements, several tiers of arches may be built between the counterforts in the form of segments of a circle.

The cordon is a round projection of stone, about a foot in diameter, which goes quite round the revêtement wall, near the top, and serves to throw the drip of rain off the face of the masonry. It is also a considerable obstacle to besiegers, in placing their ladders for escalade against the escarpe.

The profile or section of Vauban's first system is given

in Plate CCLX., fig. 4, in order to illustrate the relative relief or height of the respective works, and also to show the command which each has over the others. When the height of the rampart, including that of its parapet, is 20 feet, and that of the parapet of the covered-way is 9 feet above the plane of the site, then the rampart will have a command of 20 feet over the country, and 11 feet over the crest of the covered-way; and the latter, again, will have a command of 9 feet over the field. There are three sorts of command, namely, in front, in rear, and in enfilade. That in front is when any eminence directly faces the work which it commands; that in rear is when the eminence is behind the work; and that in enfilade is when the eminence is situated laterally on the prolongation of any line or work. The last, which is the most dangerous kind of command, is best remedied by raising the salient of works exposed to it (see woodcut 18, p. 775), or by erecting traverses. In drawing this figure, a line, called the line of site, and supposed to be the surface of the ground on which the fortification stands, is drawn, and perpendiculars are erected on it equal to the respective heights of the different parts of the works corresponding to the lines in the figure. Thus a shows the terreplein of the rampart, b the banquette or step to enable the soldiers to fire over the parapet, c the parapet, d the revêtement, e the escarpe, f the counterscarp, and so on.

2. Vauban's Second and Third Systems.

Having thus endeavoured to explain, with as much minuteness as possible, the principles of Vauban's first system, we trust, from what has been said, that no great difficulty will be experienced in understanding the methods of other engineers who have constructed works varying but little in the main from those prescribed by this system, whilst even these varieties have arisen from difference of situation and local peculiarities, more than from any other cause. The same general observation, indeed, applies to the other methods of construction followed by Vauban himself, who, in his second and third systems (Plate CCLX., fig. 2), merely modified, according to circumstances, the principles upon which the first is based. When this celebrated military engineer was called upon to repair or improve the fortresses of Landau, Brisach, and others, and found these places already surrounded with strong walls surmounted by small towers at the angles, he did not, as some might have supposed, proceed to destroy these defences, but, with his accustomed judgment and ability, he immediately took advantage of them, and constructed, nearly in the same proportions as in his first system, large counterscarsps or bastions in front of the towers which crowned the angles of the wall, just as the Italian Castrotto had done in 1584. And by this method an important object was attained; for, as in front of each tower, or rather tower-bastion, there ran a ditch which cut off all communication between it and the counterscarp, so the enemy, even if they should have succeeded in establishing themselves in the counterscarp, would still have another ditch to cross, and another wall to breach, before they could attempt to give the assault.

There is so little difference between the second and third systems of Vauban, that a description of the former will be sufficient to enable the reader to distinguish and appreciate the peculiarities of the latter. In the second system, the interior side of the polygon, from the centre of one tower-bastion to that of the next, is supposed to be equal to 240 yards, and from its extremities, at the distance of 24 yards, perpendiculars are erected equal to 36 yards, for the flanks of the tower-bastions. A line is then drawn parallel to the interior side AB, till it meets the oblique radius of the polygon, or line drawn from the centre of the polygon bisecting its angle, and this being done on both sides of the angle forms the tower-bastion. The oblique radius is then produced 78 yards, and lines of defence are drawn to the angle

where the tower-bastion joins the curtain or line AB. On these lines of defence, the faces of the counter-guard, or exterior bastion, are set off equal to 128 yards, and from the point forming the shoulder, flanks are directed to a point set off on the line AB, at the distance of 70 yards from its extremities. From the salient angles of the tower-bastions arcs are described with a radius of 14 yards for the breadth of the ditch, and tangents to these arcs are drawn parallel to the faces of the tower-bastion, but stopped where they would meet a line drawn from the salient angle of the tower-bastions, at the distance of 20 yards from the flanks.

The tennaille is the same as in the first system, excepting that, at its ends, it is carried down till it meets the line drawn between the flanked or salient angles of the tower-bastions. The ditch in front of the counterscarsps, or, in other words, the main ditch, is constructed in the same manner as in the first system. The ravelin is formed by setting off 90 yards from the re-entering angle of the counterscarp, and directing its faces to points set off on the counterscarsps, at the distance of 20 yards from the shoulders. A flank is formed by cutting off the corners of the ravelin at the distance of 14 yards on its demigorge, and 20 on its face; and this flank serves for the placing of guns in such a manner that their fire may be directed into the counterscarp, or into the ditch before them, as occasion may require. Again, at the distance of 48 yards from the re-entering angle of the counterscarp, lines are drawn parallel to the faces of the ravelin for the redoubt; a ditch is formed in front of this, and parallel thereto, about 18 feet in breadth; and the redoubt thus constructed has a command of 4 feet over the parapet of the rampart, as the tower-bastions have over the counterscarsps. The covered-way and glacis are formed as in the first system. It sometimes happens that redoubts are constructed in the re-entering places of arms; in which case their demigorges are made from 15 to 40 yards, and their faces set off at an angle of 100 degrees, as before.

3. Cormontaigne's System.

The difference between the systems of Vauban and Cormontaigne may easily be discovered by an examination of Plate CCLX., fig. 3. Vauban makes the faces of his bastions two-sevenths of the exterior side, and Cormontaigne one-third. Vauban, in his first system, produces the faces of his ravelin to the distance of 11 yards upon the face of the bastion from the shoulder, and in his second and third systems, to the distance of 20 yards; but Cormontaigne makes the capital of his ravelins about 120 yards, and produces the faces to the distance of 30 yards from the shoulder; by which means the flanks are better covered, and the bastions and ravelins are enlarged. And this is an advantage; for he is thus enabled to construct a larger redoubt in his ravelin, the curtain and flank are also better covered, and, as the former is shorter, communications are more easily kept up between the bastions. Cormontaigne gives the same breadth to his covered-way as Vauban, but he arranges in a different manner the communication round the extremities of the traverses, as may be seen by inspecting the plate. By this zigzag line of communication, which resembles the cremaillère trace adopted by Speckle in his covered-way, the passage round the extremity of one traverse may be defended by the fire of the other in its rear, or nearer to the body of the place, and the advance of assailants along the covered-way completely checked. As Speckle planned in 1589, or long before the invention of ricochet fire by Vauban had rendered traverses an essential element in fortification, his object was not the same as that of Cormontaigne, but simply to ensure a more perfect flanking defence of the branches of the covered-way than that afforded by the places of arms of his systems. The ditches are, as shown in fig. 3 of this Plate, on different levels—the main ditch being about 23 feet deep, the ditch of the re-

Fortification. doubt of the ravelin only 7 feet, so that from this latter ditch there is a fall of 16 feet to the main ditch, rendering it impossible to attack the ravelin by its gorge without the aid of ladders. An examination of the several figures which represent Vauban's and Cormontaigne's systems, as also the outworks of fig. 3, Plate CCLXI, will at once render evident the vital defect of the ordinary arrangements of outworks—that they expose by their ditches the scarp of either the body of the place, or of the work on which their faces or branches are directed, to be breached. In the system of Cormontaigne, as well as in the modern system next to be considered, the increased projection of the ravelins, by throwing the intervening bastion into a deeply re-entering position, secures it from attack by approaches until the salients of the ravelins have been taken; but this great advantage is diminished by the power of breaching the bastion from the glacis through the opening afforded by the ravelin. For the purpose of covering the communication to the re-entering place of arms, a demi-caponnière, or work composed of a parapet and glacis, was thrown across the ditch of the ravelin, as shown in the figure of the modern system, Plate CCLXI, fig. 2. This work afforded cover also to troops assembling preparatory to a sortie upon the enemy when making the passage of the ditch, but, from the depth of the ravelin ditch, it was insufficient to mask the revêtement of the bastion behind it. It will presently be shown how this object was afterwards effected; and it may be fairly said that without any material change as to system, the general result of Cormontaigne's variations from Vauban's trace is an unquestionable improvement.

4. The Modern System.

The modern system, which is shown in Plate CCLXI, fig. 2, varies but little from Cormontaigne's. Its perpendicular is one-sixth of the exterior side, and the faces of the bastions are one-third. The flanks are at right angles with the lines of defence, whereas in Vauban's system they form an angle of about eighty-two degrees; which is not so good, because, in the modern system, the guns placed in the flanks can fire straight along the ditch without being moved or turned on their platforms. The ravelin is formed by setting off thirty-four yards from the shoulder angle of each bastion along the face, which line forms one side of an equilateral triangle, the vertex of which, opposite the centre of the curtain, forms the salient angle of the ravelin. The redoubt of the ravelin is formed by drawing its faces parallel to those of the ravelin from the shoulder angle of the parapet of the bastion; and it has flanks with a ditch about twenty yards in breadth. The cavalier in the bastion is drawn parallel to the faces of the bastion, at the distance of forty-eight yards. The ditch on the faces is ten yards in width, but there is no ditch on the flanks. The couverture connected with the cavalier retrenchment is drawn perpendicular to the faces of the bastions, at thirty-four yards for the counterscarps of the coupures, whilst the scarps are at ten yards, and parallel to these. This system originated in the School of Military Engineering instituted at Mézières in 1750, and was for some time called the System of the School of Mézières. It has, however, been successively much improved; and the system which is now recognised as the modern system is that of General Noizet. Referring, however, to fig. 2 of the Plate, it will

be seen that coupures have been introduced on the faces of the ravelin; and as the ditch of the ravelin in this system has by many engineers been sunk less by 7 or 8 feet than the main ditch, there is a sufficient fall between the two to check the enemy in his passage to the latter, whilst the demi-caponnière is raised so much higher, and therefore begins to mask more effectually the revêtement of the bastion. In General Noizet's system this demi-caponnière is formed into an elevated mask, which effectually secures the revêtement from the breaching effect of the fire from the enemy's battery on the crest of the ravelin glacis. This is shown in the annexed woodcut; and the system mo-

Fortification.

Scale of Metres = 4/10,000

Fig. 28.

modified from the former modern system in this respect, as well as in other arrangements, is now the normal bastioned

Fortification. system of all the French schools. In General Noizet's arrangement the flanks are not made perpendicular to the lines of defence, but, as in Vauban's first system, the flank forms an angle of about 80° with the line of defence. In the citadel of Ghent, which is a most beautiful example of this system, with still further modifications, the retrenchment of the bastion is so formed as to take advantage of this construction, and the flanks being casemated and pierced in both directions, they become on one side the flanks of the retrenchment, whilst on the other they are the ordinary flanks of the bastion, thus giving a much longer curtain to the retrenchment than in the form exhibited in fig. 3 of Plate CCLXI, as it occupies the whole gorge of the bastion.

5. Outworks.

Plate CCLXI, fig. 3, shows several kinds of outworks, as a horn-work g, tenaillons k and h, bonnet d, lunettes a and d, an entrenched bastion e, batardeau f, and caponnière h. These, and other works of a similar description, are constructed for the purpose of occupying some of the ground which might otherwise be of service to the besiegers, or as in the caponnière to cover a communication; but their application must of course depend upon certain localities, and the judgment of the engineer must therefore determine, in each particular place, which is best adapted to the ground, and most proper to be employed with reference to the general defence of the place.

ARMAMENT OF FORTRESSES.

Having thus described, though briefly, the systems of fortification which, mainly depending on the principles first adopted by the early Italian engineers, may be considered the result of the gradual development of these principles in the more mature and skilful arrangements of successive engineers, it is right before describing other systems to say a few words respecting the means of defending a place after it has been fortified. And here we may observe, that it is difficult to lay down any exact rules as to the proportion of ordnance, ammunition, and stores of every kind required for the defence of a fortified place, seeing this must necessarily vary according to the particular situation of each fortress, the system on which its works have been constructed, and the species of attack to which it may be exposed. If, for example, one of the sides be covered by a morass, swamp, or any other obstruction which it is difficult or perhaps impossible to surmount, it must be obvious that, in this case, a smaller proportion of artillery will be required than if the fortress were equally accessible on every side; and, on the other hand, a maritime fortress, accessible at all points, will necessarily require for its defence a larger proportion of ordnance than if it were only assailable on one or a few of these points. Where every front is equally exposed to attack, all must of necessity be equally prepared.

On this subject, however, there have been established certain maxims, of which the following appear to be the most important: First, the proportion of ordnance, ammunition, and stores, should never exceed the quantity necessary for a brave and resolute defence. Secondly, those points which are considered as being most exposed to attack should be most completely armed, whilst the partial armament of the remaining points may suffice. Thirdly, for each of the faces of the bastions which are liable to be attacked, five or six pieces of ordnance should be allotted; for each of the flanks of these bastions, four; for the faces of the ravelins, from five to seven; for the lunettes, when there are such, four pieces of ordnance should be reckoned; besides two or three pieces for each of the places of arms in the covered-way. Supposing, therefore, that one front of a place is to be completely armed, the

proportions of ordnance required will be, for the faces of the bastions from ten to twelve pieces, for the two interior flanks from six to eight, for the faces of the ravelins from five to seven, and for five places of arms from ten to fifteen; making the total of ordnance for one front from thirty-one to forty-two pieces. Fourthly, when a place is exposed to attack on two consecutive fronts, the armament of each should be augmented one half; when it is threatened with attack on detached fronts, the armament should, in that case, be doubled. Fifthly, each of the other fronts should merely be provided with such a proportion as to secure it against insult. Lastly, from the foregoing maxims, it appears that a hexagon, having only one front exposed to attack, requires from fifty-eight to sixty-eight pieces of ordnance on such front, whilst in more extensive places, six, eight, or ten pieces should be added for each additional front. For the present increased power of the ordnance brought into the field this proportion should be increased by about $\frac{1}{10}$ th of the total number.

The next consideration is the proportion which the several kinds of ordnance should bear to one another. And here let it be remembered that ordnance of the higher calibre is not the only description which ought to be employed. In many cases medium and even light guns are more efficacious; for when only troops or working parties are to be fired at, light guns will answer every purpose, as the range of the shot is nearly equal to that of larger guns, and they are of course much more manageable, and may be worked with greater rapidity. But short guns of heavy calibre are best adapted for the flanks; and, generally, the large or heavy ordnance should only be employed to destroy the besiegers' batteries and dismount their guns. The flank guns being only required for the defence of the ditch, short pieces of large calibre, as carronades, which throw a heavy charge of grape or canister shot, are the most proper to be employed. The light guns, as they can easily be withdrawn, should be placed on the covered-way and places of arms, and on outworks of every description. The heavy long guns and mortars, as they are not so easily moved, should be within the body of the place, and as they require a great quantity of ammunition, they should be less frequently used, and only upon urgent occasions. A judicious economy of ammunition is a duty incumbent upon every governor or commandant of a fortified place attacked. The conduct of General Chassé in the defence of the citadel of Antwerp was a model in this respect. From the commencement till the close of the attack, scarcely a single shot was needlessly expended by the garrison.

ATTACK AND DEFENCE OF FORTIFIED PLACES.

Having thus treated of that important branch of fortification which is denominated permanent, and which, being applied solely to the defence of towns, is not liable to be destroyed except by an enemy, we now proceed to consider the attack of fortified places, the general system of which was introduced by Vauban, and so far perfected by that great engineer that it has ever since served as a model for the plans of his successors.

"La résolution des sièges," says the Mareschal, "est une affaire de cabinet. Elle est une suite naturelle de la supériorité que l'on croit avoir sur ses ennemis; mais leur exécution étant une des plus sérieuses, des plus importantes, et des plus difficiles parties, elle demande aussi le plus de mesure et de circonspection." He then goes on to state that the success of sieges depends on several circumstances, such as, "1. Du secret, sans lequel il est difficile de réussir; 2. Des forces que l'on a sur pied pour attaquer les places des ennemis, et défendre les siennes; 3. De la disposition des ennemis; car s'ils sont réunis, et aussi forts que nous, ils peuvent nous empêcher d'en faire; 4. De

Fortification. l'état des magasins les plus à portée des lieux sur lesquels on peut entreprendre: 5. De la conjoncture des temps, parce que tous ne sont pas propres aux sièges, et rien n'étant plus ruineux que ceux d'hiver, on les doit éviter tant qu'on peut: 6. Des fonds nécessaires à leurs dépenses; car l'argent est le nerf de la guerre, sans lui on ne sauroit réussir en rien. Ce sont là des mesures à prendre de longue main, qui doivent être dirigées à loisir; et après tout cela, quand on croit les avoir bien prises souvent tout échappe; car l'ennemi, qui n'est jamais d'accord avec vous, pourra vous interrompre.... Il faut bien peser toutes ces considérations, avant que de se déterminer; et prendre toujours si bien son temps, que l'ennemi ne puisse vous tomber sur les bras avant vos établissemens.¹

A siege, therefore, being one of the most arduous undertakings in which an army or corps d'armée can be employed—one in which the greatest fatigue, hardships, and personal risk are encountered, and in which the prize can only be won by complete victory; it is obvious that, upon the success or failure of such an enterprise may depend the fate of a campaign, sometimes that of an army, and perhaps even the existence of a state. Of this the failures before Pavia in 1525, before Metz in 1552, before Prague in 1557, before St Jean d'Acre in 1799, and before Burgos in 1812, present instructive examples. By the first, France lost her monarch, the flower of her nobility, and all her Italian conquests; by the second, she was saved from destruction, whilst thirty thousand of her enemies perished; by the third, the greatest warrior of his age, Frederick the Great, was brought to the very brink of destruction; by the fourth, the most successful general of France, and perhaps the greatest commander that any age or country has produced, was stopped short in his career of victory; and by the last, a beaten enemy gained time to recruit his forces, concentrate his scattered corps, and regain that ascendancy of which the victory at Salamanca had for a time deprived him. Innumerable other instances of the disastrous consequences usually attendant on the failure of sieges might easily be produced; but those which have just been referred to are sufficient to establish the importance of the undertaking, and to show that the dearest interests of a country may frequently be staked on the sure and speedy reduction of a fortress.

It is therefore of the greatest importance to a state that the sieges undertaken by its armies should be carried on in the best and most efficient manner possible, or, in other words, that by a due combination of science, labour, and force, these operations should be rendered not only short, but certain, and unproductive of any great expenditure of life. But the sieges undertaken by the British have almost never united these three indispensable conditions; and with regard to those which took place during the contest in the Peninsula, it is well known that various defects of organization, and particularly the want of a body of men such as sappers and miners, trained to the labour required at sieges, and an inadequate supply of matériel, necessitated a partial departure from established principles and rules of attack, and consequently led to a waste of life wholly unprecedented in modern sieges. Till late in 1813 the army was unattended by a single sapper or miner: regular approaches were therefore difficult if not impracticable: it was necessary, in almost every case, to take the bull, as the saying is, by the horns; the last operation of a siege scientifically conducted, namely, battering in breach, was amongst the first undertaken: and the troops were marched to the assault whilst the defences remained nearly entire, and exposed to every species of destruction which the unreduced means of the besieged could bring

to bear against them. The army of a country which has outstripped all others in the useful arts and in mechanical improvements, was left wholly unprovided with those appliances which at once economise labour and life, and serve to render both most effectual for the purposes to which they are applied. But, notwithstanding this great anomaly, which is chargeable against the government alone, and not against either the nation or the army which in the most adverse circumstances so nobly sustained its reputation, it may be observed that, in all periods and in all countries, the means employed for the reduction of fortresses have generally increased and become more overwhelming and irresistible in proportion to the advancement of knowledge and the improvement of the useful arts; and that in Europe during the last two centuries, the extensive diffusion of wealth and knowledge, accompanied by an unprecedented development of talent, all more or less directed towards military movements, has caused the results of sieges, and indeed of almost all the operations of war, to depend much less on individual exertion or casual displays of heroism, than on mere combination and expenditure. This may be made apparent by a slight retrospect of the sieges of the sixteenth century.

At the period here referred to, the art of disposing the several works of a fortress so as to cover each other, and to be covered by their glacis from the view of an enemy, was either unknown or disregarded; whilst the small quantity of artillery in use, its unwieldiness, and the great expense and difficulty of bringing it up, occasioned so little to be used in sieges, that the chief object in fortifying towns was to render them secure against escalade and surprise, by means of lofty walls or altitude of situation. All places fortified prior to the sixteenth century are invariably of this construction. And as the simplicity of the fortresses to be attacked necessarily gave the same character to the operations directed against them, so, in those days, everything was effected by daring courage, without the aid of science; and gallantly contending in individual combat, or fearlessly confronting danger, were considered as the highest qualities of a besieger. Thus the contest dragged on for months, in petty but sanguinary affairs, and the most persevering or the most hardy troops, however ill organised or supplied, were the most dreaded, and not unfrequently the most successful. But when artillery became more moveable, and large quantities began to be employed in sieges, lofty and exposed walls no longer opposed any adequate barrier; large breaches were speedily effected; places which had formerly resisted for months were carried in a few days; and hence, in order to restore an equality of defence, it became necessary to screen the ramparts from distant fire. The attempt to gain security by concealment rapidly advanced towards perfection, whilst the means of the besiegers remained the same; and between the middle of the sixteenth and commencement of the seventeenth century, works were so skilfully disposed and so well covered, that the defence of towns obtained a temporary superiority over the attack as the latter was then practised. Of this the obstinate and successful defences made by the Dutch against the Spaniards during the reigns of Philip II. and Philip III. may be cited as remarkable examples.²

The pre-eminence of the defence over the attack was mainly due to the great difficulty of dragging up heavy ordnance with a besieging army, so that the weight of metal being generally in favour of the besieged, the fire of the fortress was enabled to keep in check that of the batteries of attack. Vauban, however, in the reign of Louis XIV., restored the preponderance of power to the attack by the invention of ricochet fire, as the guns of the besieged were

¹ De l'Attaque et de la Défense des Places, pp. 1 and 2. Hague, 1737, 4to.

² Journals of Sieges in Spain, by Colonel Sir John T. Jones; Preliminary Observations on the Attack of Fortresses.

thereby dismounted or disabled at an early stage of the siege, and the besiegers were enabled to push forward their approaches by the sap, being relieved in great measure from the dangers and difficulties of a direct and powerful opposing fire of artillery. Vauban also matured into a system the attack by laying down rules for the establishment of parallels, for the location of enfilade and other batteries, and for the general conduct of the approaches. The real type of an attack is a moving parapet, the besieger carrying on with him his cover, and thus depending for his success not so much on his offensive as on his defensive arrangements. It was by this combination of science and labour, aided by the steady advances of brave and well-trained sappers, that the reduction of fortresses, which would have resisted for ever the rude assaults of the most determined enemy, was rendered comparatively easy and certain.

These increased means of attack, to which it was found impossible to oppose a successful resistance, caused the art of concealment or covering to be further studied, till at length, in well-constructed fortresses, not a single wall remained exposed to view, and the sap and the mine became as necessary as the gun and the mortar to the success of a besieger. To render this intelligible to the general reader, it may be proper to introduce here a descriptive sketch of the progress of a modern attack, from the excellent work of Sir John Jones, already referred to.

"The first operation of a besieger," says that able and experienced engineer, "is to establish a force able to cope with the garrison of the town to be attacked, at the distance of six or seven hundred yards from its ramparts. This is effected by approaching the place secretly in the night with a body of men, part carrying entrenching tools, and the remainder armed. The former dig a trench in the ground parallel to the fortifications to be attacked, and with the earth that comes out of the trench raise a bank on the side next to the enemy, whilst those with arms remain formed in a recumbent posture, in readiness to protect those at work, should the garrison sally out. During the night this trench and bank are made of sufficient depth and extent to cover from the missiles of the place the number of men requisite to cope with the garrison, and the besiegers remain in the trench during the following day, in despite of the fire or sorties of the besieged. This trench is afterwards progressively widened and deepened, and the bank of earth raised till it forms a covered road, called a parallel, embracing all the fortifications to be attacked; and along this road, guns, wagons, and men securely and conveniently move, equally sheltered from the view and the missiles of the garrison. Batteries of guns and mortars are then constructed on the side of the road next the garrison, to oppose the guns of the town, and in a short time, by superiority of fire, principally arising from situation, silence all those which bear on the works of the attack. After this ascendancy is attained, the same species of covered road is, by certain rules of art, carried forward, till it circumvents or passes over all the exterior defences of the place, and touches the main rampart wall at a spot where it has been previously beaten down by the fire of the batteries erected expressly for the purpose in the more advanced parts of the road.

"The besiegers' troops being thus enabled to march in perfect security to the opening or breach in the walls of a town, assault it in strong columns; and being much more numerous than the garrison defending the breach, soon overcome them, and the more easily as they are assisted by a fire of artillery and musketry directed on the garrison from portions of the road only a few yards from the breach; and which fire can, at that distance be maintained on the defenders of the breach until the very instant of personal contention, without injury to the assailants. The first breach being carried, should the garrison have any inner works, the covered-road is by similar rules of art pushed forward through

the opening, and advanced batteries are erected in it to overpower the remaining guns of the place; which effected, the road is again pushed forward, and the troops march in security to the assault of breaches made in a similar manner in those interior works, and invariably carry them with little loss. But as it is always an object to preserve the life of even a single soldier, so, when time is abundant, the loss of men attendant on the assault of breaches under these favourable circumstances may be avoided, by pushing up the covered-road through the breach, without giving the assault, and thus, by art and labour, the strongest defences frequently fall without any exertion of open force."

From this description it must be obvious that the most important object at a siege is to carry forward the covered-road to the walls of the place; that all the other operations are secondary to and in furtherance of such an advance; and that hence the efficiency of armies at sieges depends upon their ability to complete the road at a small expense of life. But in forming this covered-road, different degrees of difficulty are experienced in proportion as it advances. At its commencement, the work being about six hundred yards from the fortifications, can easily be performed by the common soldiers. But when the road or trench has arrived within a fair range of musketry, or three hundred yards from the place, then particular precautions are required; yet the work at this stage is not so difficult as to prevent its being executed by soldiers who have had a little previous training. At the last stage, when the approaches have been pushed close to the place; when to be seen is to be killed; when mine after mine blows up the head of the road, with every officer and man on the spot; when the space becomes so confined that little or no front of defence can be obtained; and when the enemy's grenadiers sally forth every moment to attack the workmen, and deal out destruction to all less courageous or weaker than themselves; then the work becomes truly hazardous, and can only be performed by selected brave men, called sappers, who have acquired the difficult and dangerous art from which they derive their name. An indispensable auxiliary to the sapper, however, is the miner, who, in the exercise of his art, requires even a greater degree of skill, conduct, and courage. The duty of a miner at a siege is to accompany the sapper, to listen for and discover the enemy's miner at work, and to prevent his blowing up the head of the road, either by sinking down and meeting him, in which case a subterranean conflict ensues, or by running a gallery close to that of his opponent, and forcing him to desist from working by means of suffocating compositions, and various arts of chicanery, the knowledge of which he has acquired from experience. Without the aid of skilful miners, sappers would be unable to execute that part of the covered-road forming the descent into the ditch, not to mention other operations in the progress of which the assistance of the miner is equally indispensable; and without their joint labours and steady co-operation, no besiegers' approaches ever reached the walls of a fortress. In the British service, indeed, they are blended into one honourable body, the Sappers and Miners.

But a siege, though it calls for great personal bravery, unremitting exertion, and extraordinary labour in all employed, yet, if scientifically prosecuted, is alike certain in its progress and its result. More or less skill and exertion in the contending parties may in some degree prolong or abridge its duration; but the sapper and the miner, when skilfully directed and adequately supported, will ultimately surmount every obstacle. On the other hand, sieges undertaken by armies imperfectly supplied with these auxiliaries, as the British army once was, are hazardous in the extreme. Their only chance of success consists in scrutinizing the exterior of a fortress, in order to discover some spot whence, from the irregularity of the ground, or fault of con-

Fortification. struction, the main escarpment wall may be seen at a distance sufficiently great to enable the ordinary working parties to approach with the covered-road, and there to establish batteries for breaching the wall or forming an opening through it into the place. When this is effected, the troops at once advance to the assault of the breach, as in the sixteenth century, thus losing the shelter of the covered-road at the moment when the fire of the place becomes most powerful and destructive; and as the fire of the besieger's distant batteries is necessarily suspended during the assault, in order to avoid killing their own storming party, the garrison can therefore with impunity mount their ramparts and employ every kind of weapon, missile, and instrument in their defence. All the chances are thus in favour of the besieged; for should the columns of attack, under all these disadvantages, arrive in good order at the brink of the ditch, they must descend into it by a wall from fourteen to sixteen feet in depth, which cannot fail to break their order and throw them into confusion; and as no new formation can be attempted in a spot where death is incessantly showering down on them, the assailants rush to the breach more like a rabble than a solid column. From this moment success hinges on the individual and confident bravery of the officers and troops, and the unshrinking firmness of the general commanding, in at once encouraging and supporting their efforts. But although these qualities, when united in a high degree, may, at a great sacrifice of life, enable the assailants to overcome all resistance, yet an assault of this nature, attempted under ordinary circumstances and feelings, has almost invariably proved unsuccessful. Indeed it may be laid down as the general result of experience, that should an army unprovided with sappers and miners, and the necessary materials and means to render their services efficient, be opposed to a place fortified according to the modern system, with its walls completely covered, all the usual methods to reduce it would prove unavailing; no period of time nor sacrifice of men would be sufficient to purchase success, and the prudent course would be to decline an attempt pregnant with hazard, perhaps ruin.

"These considerations," says Sir John Jones, to whom we are indebted for the above account of the various modes of attacking fortified places, "have for many years had their due weight with the great powers of Europe, and induced them to form and keep up, as integral portions of their military strength, every necessary auxiliary for the reduction of fortresses; and their sieges have in consequence become certain and comparatively bloodless. But England, constitutionally jealous of permanent military establishments, always discountenanced military organization and military preparation till the hour of need; and with respect to sieges, they being of rare occurrence, and moreover exclusively offensive operations, even carried her jealous feelings beyond the bounds of rational prudence; for, possessing a corps of officers professionally educated and well grounded in the science of attack and defence, she denied them every requisite establishment to render their acquirements availing, and most unreasonably expected her armies to reduce the skilfully fortified and well-covered places of the nineteenth century with means inferior to those brought against the exposed and ill-constructed places of the sixteenth and seventeenth centuries." And what was the immediate consequence of this irrational jealousy and niggardly parsimony? Contrary to all ordinary calculation, the fortresses garrisoned by the French in Spain were reduced; but at what a prodigious expenditure of life was this effected? In the several attacks upon Badajoz, two of which, from extrinsic circumstances, proved abortive, a little army was sacrificed; as many men, in short, as would have been sufficient for the consumption of ten sieges undertaken with adequate means, and conducted according to the ordinary rules of science. But this is not to be understood as involving any reflection

against the military talents of the general or the professional ability of the engineers. General Foy, in his work on the war in the Peninsula, has indeed made such a charge, condemning the mode of attacking fortresses adopted by the British in Spain as unskillful and inefficacious, and bringing it forward as indisputable proof of the low state of military knowledge in our army. But it should be recollected that the adoption of this mode was not a matter of choice, but of necessity; and that if it was in its own nature rash, hazardous, and inefficient, the fact of its having been directed against Ciudad Rodrigo and Badajoz with such rapidity of development and certainty of result as to outstrip the calculations of the French marshals, deceive the vigilance of French governors, paralyse the science of the French engineers, and baffle every defensive effort of the French garrisons, is surely no evidence of deficiency in military talent and professional skill. The objections to this mode of attack are insurmountable and decisive; that it succeeded in the instances referred to is merely a proof what British soldiers, even when acting under the greatest disadvantages, are capable of accomplishing. The force of the remarks of Sir J. Jones has not become less by the progress of time, as the present war found us, not indeed so deficient in well-trained sappers as we were at the commencement of the last, but equally so in all the most important elements of modern organization, and, as regards this special branch of the service, not yet determined as to what the field equipment of the engineer establishment ought to be. We have still to learn the importance of that scientific knowledge which would enable the engineer to vary that equipment so as to meet the necessities of the geological structure of each particular country.

Having thus given a general description of the methods of attack, we shall now subjoin, on high authority, a view of what is considered as necessary for the proper defence of fortified places. An order issued by the French minister of war in 1813 contains directions on the subject which are almost universally applicable, and therefore deserve a place here. Every commander is directed to consider his garrison as liable to be unexpectedly attacked, and to pass at once from a state of peace into one of war or siege, either by rebellion, by unlawful assemblies, by the presence of an enemy, by surprise, or by sudden assault; in a word, by unforeseen causes, of which the history of war offers numerous examples. He is therefore ordered, even in time of peace, to fix his plan and arrangement for defence, according to such supposed attacks as may appear most probable, and to determine, for the principal cases which may be likely to occur, the necessary posts, reserves, and movements of the troops, and to take measures to ensure the due and active co-operation of every corps of the garrison. He ought, particularly, to make himself thoroughly acquainted with, first, the ground beyond the place which may be within the circle of action, of investment, and of attack; secondly, the fortifications of the place, its interior, its buildings, its military edifices or establishments; thirdly, the garrison, the means of the place in artillery, in ammunition, and in other stores of every kind; fourthly, the population to be subsisted in time of siege, the men capable of bearing arms, the master and journeymen artificers fit to be employed either on the works or in case of fire; and, fifthly, the provisions, materials, tools, and other resources which the town itself and surrounding country can furnish, and which it might be necessary to secure in case of siege. In order to enable governors and commanders to comply with these instructions, which are equally clear and precise, the minister proceeds to detail their principal duties, according to the circumstances in which they may find themselves placed; but for these we must refer to the general order itself, which is a masterpiece of its kind, and in all probability emanated directly from Napoleon himself. Its object appears to have

been to inspire a governor with hopes, that by taking proper precautions, and making a full use of means previously provided, the defence might be rendered equal, if not superior, to the attack; and although it is still considered that the idea of attaining such an advantage for the defence is far from being realised, yet the importance of the directions embodied in the order is not on that account diminished, and where they are duly observed, the nature and extent of the resistance must be materially increased.

The protracted and able defence of Sebastopol will doubtless lead many to doubt the accuracy of the opinion thus stated, and to imagine that the Russians have by some new defensive arrangements solved the problem so long under discussion, and again restored to the defence its former superiority over the attack. This idea has indeed so taken possession of the public mind, that already persons have been found ready not only to assert the supposed fact, but also to explain the mode in which the improvement has been effected: whenever Sebastopol shall fall, and as regards the southern defences, the period of such fall seems approaching, this delusion will doubtless be dispelled, and the real merits of the Russian engineers will be found to consist not in the discovery of new principles, but in the skilful application of those principles which, recognised at an early period, have been by degrees matured and enlarged. In estimating the comparative results of the attack and defence of Sebastopol, it must also be remembered that neither can be judged by strict rules, as neither has conformed to such rules. The north side being left open by the impossibility of fully investing the whole line of defences, the south became a detached line of powerful intrenchments, upon which the whole force of an army, not of a garrison, could be directed at will in its defence. In another point, also, the attack has not had its usual advantage, not having been able to use, with the customary effect, the enfilading ricochet fire, as the disposition of the line of works was such as not to offer sufficiently salient points, and therefore to leave so much to be done by direct fire. The unlimited extent of the garrison, being capable of continued renewal from the external army, has permitted the use of detached forts or works which, when backed by a line in rear of them sufficiently strong to resist a coup-de-main, constitute one of the most powerful modes of defence. Such a fort or work is the celebrated Malakoff Tower, and the redoubt enveloping it, the type of which may be found in the Lunette of Darçon, of which fig. 39 is a plan. In this lunette,

Fig. 39.

intended to be prepared beforehand, T is a powerful tower, LL a lunette, in this case revetted, but which might have been made, as at the Malakoff, a simple earth-work—an underground communication to gg, loopholed galleries for flanking the ditches. This little sketch will show the general principle of defence involved in such works, but of course the form must vary in the hands of an able engineer, so as to suit the peculiarities of the ground. At the Malakoff the redoubt has been made circular, but as to principle it is strictly analogous to the lunette. Hereafter, without doubt, the details of this remarkable siege will become the study of military men, but at present it is necessary to select some

other example, as there is as yet far too much uncertainty as respects the exact form, construction, and position of the works of Sebastopol to enable an engineer to reason with certainty upon them.

For the elucidation, then, of the attack, we shall now proceed to give a sketch of the attack on the citadel of Antwerp; first, because this was the most regular and scientific siege which had taken place for many years; and, secondly, because, as a practical operation, an account of it must not only be more interesting, but at the same time more instructive, than any description whatsoever of the formal theoretical plans which are usually drawn in the military schools.

The French army employed to cover and conduct the attack of the citadel of Antwerp, in November and December 1832, was placed under the command of Marshal Gerard, and amounted to 54,000 infantry, 6000 cavalry, and 6450 engineers, artillery, and pontooniers, making a total of 65,450 men, and 14,300 horses, with 144 pieces of siege, and 78 of field artillery. On the 24th of November Marshal Gerard established his head-quarters at the village of Berchem, about 2500 yards from the citadel, and issued orders to commence operations in the evening as soon as it became dark. The garrison of the citadel, under General Baron Chassé, amounted to 4470 men, with 144 pieces of ordnance of all calibres, and abundance of ammunition and stores.

It will be observed here that a garrison of about 5000 men was opposed to the attack of a besieging army thirteen times its strength.

At eight o'clock p.m. on the 29th November the French troops destined for this service consisted of 18 battalions, 900 artillery, and 400 sappers, in all about 17,140 men, assembled at the depôts of intrenching tools. The flank companies of these brigades, supported by twelve eight-pounders and a strong piquet of cavalry, formed the covering party under the direction of General Haxo, by whom and the officers of his department (the engineers) the first parallel and approaches were traced out, whilst General Niegre and the officers of artillery marked the sites of the projected batteries. The first parallel leaned on the covered-way of the right face of Montebello, and extended towards Kiel, its nearest point being about 325, and its farthest 435 yards from the advanced front of the citadel. The distance covered by the first parallel, from right to left, was 1870 yards, and that by the approaches 3750 yards. The communications from the right and centre debouched from the Malines Chaussée, in the village of Berchem, parallel to the road leading from that village to the Harmony and St Laurent; that from the left commenced near to the garden called Heinrich's; whilst a fourth, on the extreme right, sprung from the covered-way of the left flank of Montebello, opposite to the first traverse.

On the second night, from 30th November to 1st December, five approaches were pushed on in front of the first parallel; two in the direction of the capital of the Toledo bastion, two upon that of the Lunette St Laurent, and one, being the fifth, terminating in a place of arms on the extreme left. From the 1st to the 2d December two zigzags were added to the approaches; one from the centre, in the direction of the gorge of St Laurent, and the other on the right, diverging towards the curtain, between the Toledo and Fernando bastions. The badness of the weather sadly incommoded the workmen, and prevented the artillery getting the guns into battery. Between the 2d and 3d December four zigzags were made in front of the approaches on the right and centre, and half a parallel was formed to complete the place of arms constructed on the left during the night of the 30th November. The heads of the zigzags were pushed to within 135 yards of the glacis. The batteries Nos. 1, 2, 3, 4, 5, 6, and 9, with two for mortars

Fortification. in the rear, were armed, and ready to be unmasked at a moment's notice. The arming of Nos. 7, 8, and 10, on the extreme left, was impeded by the difficulties of the ground. From the 3d to the 4th December, the second parallel was traced and commenced, its right leaning on the foot of the glacis of the counterguard, its centre and right 130 yards distant from the place of arms in the covered-way of the Toledo bastion, and its left towards the right of the covered-way of St Laurent, at 90 yards from the crest, and 15 from the foot of its glacis. The length of the second parallel was 1250 yards, and, together with its approaches from the first parallel, it occupied 3025 yards of ground. By the greatest exertions batteries Nos. 7, 8, and 10 were armed during the night. This completed the armament, and, at 11 A.M. on the 4th, the embrasures were unmasked, and the signal being given, the batteries opened their fire from centre to flanks, and maintained it steadily during the day.

From the 4th to the 5th of December an approach was pushed on from the second parallel, almost in a direct line upon the salient angle of St Laurent, and an entry was made into the covered-way by a return to the left. The garrison discovered this, and opened a sharp fire from the lunette; a lodgment was, however, effected near the spot usually occupied by the first traverse. At this time the garrison suffered much from the fire of the besiegers. From the 5th to the 6th the lodgment made the previous night in the covered-way of the salient place of arms of St Laurent was prolonged as far as the first traverse. But the besieged kept up so vigorous a fire that the French engineers were obliged to renounce the flying and adopt the full sap. The zigzag in the counterguard, being about three feet in width and four in depth, was conducted along the parapet, nearly to the extremity of the right flank, and within 180 yards of the counterscarp of bastions Toledo and Fernando; and two lodgments, blinded with fascines, were made in the parapet for six rampart guns to enfilade the covered-way of the Toledo bastion. In the meantime a steady fire was kept against Kiel, the ravelin in its rear, and the Paciotto bastion. From the 6th to the 7th a battery of 24-pounders near the village of Burcht on the left and Hoboken on the right opened on the gun-boats which flanked the French post at the Melk Huys. It was intended to assault St Laurent this evening; but as the lunette was found to be too well protected by trous-de-loup, the project of storm was abandoned, and the regular method of descent, passage, and mine, determined on.

Between the 7th and 8th of December a shell penetrated the blindage of the laboratory, and setting fire to loaded bombs and other combustibles, caused considerable havoc. A battery for six mortars, E, on the right between Nos. 3 and 4, now opened its fire; another, F, also for six mortars, was traced behind the centre of the parallel; and platforms for four mortars were laid down near Montebello. The fire of these batteries was directed on the Toledo bastion and the buildings within it. On the previous day jets of smoke and flame were seen to issue from the Great Barracks, and, in spite of every exertion on the part of the garrison, the whole building soon became involved in a general conflagration, which raged with such fury, that by the evening of the 8th it was entirely consumed.

From the 9th to the 10th of December the operations against St Laurent were renewed with great activity, and the sap advanced to the crotchet of the second traverse, whilst that intended to debouch upon it from its right was likewise pushed on. The principal operation of the night, however, was the opening of the third parallel, 130 yards in advance of the second, its right debouching beyond the Boom Chaussée, from the branch running into the covered-way of the counterguard, and its left uniting with the boyau parallel to the foot of the glacis of St Laurent. At this time the garrison suffered much from the vertical fire of the mor-

tars and howitzers, especially the great mortar, and the new-model eight-inch howitzers. Until the year 1822, the eight-inch howitzer in common use in France measured three feet six inches French, and weighed 1096 lb., or twenty-three times the weight of the loaded projectile, whilst its calibre was equal to a solid shot of 80 lb., and contained 65 ounces of powder. The new-model howitzer is an improvement on the Russian licorne and the Spanish heavy howitzer, perfected by Colonel Paixhans. The raft for the blinded descent into the ditch was brought up to the lodgment, and a second descent à ciel couvert was commenced to the left of the first. The third parallel was, at the same time, improved and widened. A little after dusk on the 10th the besieged made a sortie, which was driven in, but not until damage enough had been done to occupy the French all the night of the 10th and morning of the 11th in repairing it. From the 11th to the 12th three rafts were got ready, and placed in the descents to the ditch; they were about twelve feet by eight. At dusk the miners returned to the escarp, and, in an excavation made the previous night, fixed two petards, which, by their explosion, produced a fissure in the wall; and a sergeant having immediately entered the hole, commenced a gallery under the centre of one of the arches. At 11 A.M. on the 12th the battery mortars, H, on the extreme right of the second parallel, opened their fire, which, combined with that from the others, told severely on the Toledo bastion. The miners still continued their work under the lunette St Laurent, and commenced chambers for three mines. The fourth parallel was widened during the day.

Between the 12th and 13th of December the miners were at work in the chambers under St Laurent, which were not yet completed. On the right the covered-way of the left face of the Toledo bastion was crowned to within sixty-five yards. From the 13th to the 14th, after nearly sixteen nights of open trenches, the arrangements for the assault of St Laurent were completed, and orders were issued to prepare for the storm. Much, a great deal too much, was said of this out-work, defended by little more than a hundred men, one five-and-a-half inch howitzer, two coehorn mortars, and a six-pounder. The mine being reported charged, the blinded descent into the ditch was pierced as soon as it became dark, and everything got ready for the assault. Three storming parties, consisting of the flank companies of the 65th regiment of the line, were posted in readiness, with a column of reserve; and at 5 A.M. on the 14th, every preparation being completed, the match was applied to the saucissons of the mines. After a few moments of suspense, three successive explosions took place, and the escape immediately presented a wide and practicable breach. The fascines for crossing the ditch had been injured by the explosions; but after a little delay the storming party entered almost without opposition, and made prisoners one lieutenant and forty-eight rank and file, the others having escaped into the citadel. Thus fell the lunette St Laurent.

After this operations were carried on against the citadel, and at 11 A.M. of the 21st December the battering in breach commenced, and continued for two days. At length, on the 23d, when a practicable breach had been formed, and Marshal Gerard was about to deliver the assault, the garrison surrendered, after as gallant a defence as any recorded in military history, though more remarkable for its passive than its active character. When Marshal Gerard, accompanied by the French princes, entered the fortress, they found General Chassé in a casement in the Alba bastion, which he had occupied during the siege. On their progress from the gate to the governor's quarters, they passed through a scene of desolation and ruin, intermixed with painful and disgusting objects, which baffles all description. The whole, indeed, presented an unparalleled chaos of black

Fortification. and smouldering destruction; and, with the exception of the principal powder magazine, two or three service magazines, and the hospital, not a building was standing. The terrepleins of the bastions were ploughed into deep ruts by the shells; the gorges were encumbered with heaps of fallen rubbish; and though the casemates and subterranean communications were not perforated, all of them had sustained damage from the incessant explosion of shells, and they emitted an offensive, nay, almost insupportable odour, caused by the number of men who had been crowded into these vaults. Everything was of course said by the victors to console and flatter the vanquished. When Count Gerard took his leave of General Chassé, he observed to the brave veteran, "that it was high time to surrender; that he had gallantly and honourably done his duty, and that he ought not to have held out a day longer." With a fortress reduced to a heap of ruins, a garrison exhausted and extenuated, and a breach sufficiently wide to admit a column formed upon a front of a hundred, it would not have been bravery, but madness, to attempt, under such circumstances, to stand an assault.

The following is a list of the different batteries, with the direction of their fire respectively —

No. of Batteries.	24 Pounders.	16 Pounders.	8-inch Howitzers.	12-inch Mortars.	Distance in Yards.	Direction of Fire.
Opened on the 4th and 5th December.
1	6	...	12	...	535 & 550	Battering the left face of Toledo, and gorge of St Laurent.
2	...	12	12	...	500	Ricochetting the left face of Toledo.
3	4	...	12	...	640	Battering the left face of the Ravelin.
4	...	3	12	...	650	Ricochetting left face of the Ravelin.
5	6	12	1	...	630 & 430	Battering right face of Toledo, and Ricochetting left of Toledo.
6	...	12	12	...	700	Ricochetting left face of Toledo.
7	6	12	1	...	380 & 700	Ricochetting left face of St Laurent, and battering right face of Paclotte.
8	...	3	2	...	465	Ricochetting left face of Ravelin.
9	...	...	6	...	820	Battering salient angle of Paclotte.
10	8	...	...	...	650 & 520	Battering left face of Ravelin, and Lunette of Kiel.
A	...	...	...	10	850	Not armed.
B	...	...	...	9	1000	Body of the Citadel.
C	...	...	...	11	1050	.....
D	...	...	...	10	850	.....
Between the 8th and 15th.
...	30	14	20	40	.....	.....
11	4	...	...	...	500	Battering the right face of Toledo.
12	...	3	...	...	435	Battering the Bataudeau.
13	...	4	...	...	220 & 275	Battering the left face of Ravelin.
E	...	...	...	6	500	The body of the Citadel.
F	...	...	...	6	490	.....
G	...	...	...	6	650	.....
H	...	...	...	6	380	.....
K	...	...	...	8	600	.....
14	6	...	...	...	50	Breaching Battery.
15	6	...	...	...	350	Counter-battery against the left flank of Fernando.
16	...	...	...	...	125	Six perriers on the Ravelin and Toledo.
L	...	...	...	10	250	Terreplein and rampart of Toledo.

This operation, so instructive in a military point of view, is also remarkable as having occurred in a time of general peace. It would be out of place here to enter into any detail of the complicated series of events and negotiations out of which so singular an occurrence arose: we shall therefore content ourselves with observing, generally, that Great Britain and France, as joint guarantees for the integrity and

independence of Belgium, having failed in every attempt to procure the evacuation of Antwerp by means of negotiation, were obliged, by the faith of treaties, to have recourse to force. Hence the siege, politically considered, is to be viewed merely as an ejectment executed against the king of Holland, who had refused to renounce possession, unless compelled to do so.¹ Fortification.

The French brought against this place 66,450 men, 14,300 horses, and 222 guns of all descriptions; and they lost during the siege 108 killed and 695 wounded, total put hors de combat 803. The Dutch had 4937 men in the garrison, of whom they lost 122 killed, 369 wounded, and 70 missing, total 561.

A careful comparison of the details of this siege with the general principles which have been enunciated will enable the reader to recognise the importance of the following maxims.

1. Independently of the great amount of labour to be provided for in the construction of parallels, approaches, and batteries, there will be a daily drain upon the besieger's forces by casualties, so that he can scarcely expect for success unless his original preponderance in numbers has been such as to leave him at the final moment of assault in a condition to attack the diminished garrison with an overwhelming force. In addition, therefore, to a covering army when external relief is threatened or anticipated, the besieging army should be from four to five times the strength of the garrison, or even more, should the nature of the ground, as at Sebastopol, add to the ordinary difficulties of approach. This superiority of force is necessary to give celerity and steadiness to the operations, which would otherwise be tedious and interrupted.

2. A perfect investment is not merely expedient but indispensable. So long as any portion of the enceinte of a fortress is left open or unwatched, the garrison is able to recruit its strength from without, whilst within it is relieved from that moral depression which must, more or less, oppress men when entirely closed up within a narrow space, and exposed, day after day, to fatigue and danger. Under such circumstances there seems to be no natural limit to the power of defence, as fresh supplies of men enable the besieger to go on adding intrenchment within intrenchment, and it is only possible to overcome him by determined, reiterated, and overwhelming assaults. Such have been the circumstances of Sebastopol, as the system of attack adopted by the allies has never enabled them to isolate even the southern section of the fortress, the means of communication between the south and north remaining available to this day. Without doubt fresh troops, or rather reliefs, are brought to the south side frequently, and a temporary superiority in numbers on that side given to the defenders over the immediately attacking force. It ought not, therefore, to be a matter of surprise that the progress of the siege is slow, and, to the eye of the general observer, uncertain, because so frequently interrupted.

3. Good and secure lines of communication are most essential, as there ought not to be any cause of interruption when once the ground has been broken and the siege commenced. Neither in the attack nor in the defence should guns be fired idly, or from distances and positions which would render their fire useless; but when the proper distance has been arrived at, battery should succeed battery as the works of approach advance, and no interval for rest or for repairing injuries should be allowed to the besiegers; but how can this object be ensured with roads so heavy and bad as to stop the transport of ammunition and of ordnance?

4. The importance of advanced works was strongly exhibited at the siege of Antwerp, as the whole force of the attack was directed against the advanced lunette St Lau-

¹ The account of the siege given above is abridged from that published in the United Service Journal, and which is decidedly the best that has yet appeared.

Fortification. rent, whilst the defence was good, although under the disadvantage of wanting the collateral defence of the Lunette Montebello (see Plate CCLXII.) In such a case as Sebastopol, the garrison being in fact a small army, such works must afford the best means of an obstinate defence, and, by forcing the besieger to act on the circumference of a larger circle, diminish very much his ordinary advantage of concentration.

Siege of Dantzic.

Having thus given an example of an interior and passive defence, we shall now, in further illustration of the principles already laid down, advert to one of a different if not opposite kind. The siege of Dantzic, whether considered with reference to the magnitude of the operation, the difficulties to be surmounted by the besiegers, or the active and varied character of the defence, was certainly one of the most memorable events in the campaign of 1807. Before the war of 1806 and 1807 the fortifications had been much neglected, because, from the position of the place, no one suspected that it would have to sustain a siege. But when the battles of Iena and Auerstadt had entailed destruction on the Prussian army, and laid open the kingdom, General Manstein, who commanded at Dantzic in the absence of Field-marshal Kalkreuth, the titular governor, had laboured with much activity in improving the exterior works, and particularly in causing them to be strongly palisaded. It is necessary, therefore, to describe the principal defences at the period when the place was invested by Marshal Lefebvre, at the head of the tenth corps of the grand army, and immediately before the commencement of the trenches on the 1st of April 1807.

The city of Dantzic, traversed by the Moltau, was surrounded with large ditches filled by that river, the waters of which, retained by several sluices, formed, to the eastward, a vast inundation, which, reaching on one side to the suburbs of Ohra and St. Halbrecht, and on the other to the dykes of the Vistula, extended about four leagues, and covered two-thirds of the eastern fronts. On the north the Vistula runs about 260 yards from the covered-way, leaving a space between the left bank and the glacis of the place, consisting of an impracticable marsh, intersected by some canals; and at its embouchure, distant nearly three miles, the banks were defended on the right by the fort of Weichselmunde, and on the left by an intrenched camp in the small island of Neufahrwasser, intended to cover and protect the arrival of such succours as might come from the seaward. The ground adjoining the banks of the Vistula being intersected by canals and covered with marshes, was extremely unfavourable to a besieger, as it rendered it difficult for him to form establishments or raise works of proper solidity, and forced him to extend his quarters, disseminate his troops, and multiply his posts. At the period in question this inconvenience was the more severely felt, because the besieging force was inferior in numbers to that of the garrison, and it required the most vigilant caution to occupy numerous posts without unduly weakening it. The communication between the place and the fort of Weichselmunde was maintained by a series of redoubts constructed on the borders of the Vistula, and particularly by the advantageous position of the isle of Holm, which enabled the besieged so to approximate the fire of the place to that of the fort as only to leave between them an interval of about 1400 yards, and also to communicate with Weichselmunde by the canal of Laack, in spite of batteries which the besiegers might establish at Schellmühl. The French, therefore, could not attempt to throw a bridge over this part of the Vistula until

Fortification. they had made themselves masters of the isle of Holm. On the west two chains of hills, separated by the valley of Schidlitz, covered this part of the enceinte; and the prolongations of these hills were crowned by two forts, that of Bischopsberg and that of Hagelsberg, which, being connected by continuous intrenchments, formed a second enceinte, flanked upon one side by the inundation of the Moltau, and upon the other by the left bank of the Vistula. This new enceinte, though constructed of earth, and without revetement, was nevertheless secure against insult; and as the covered-way, as well as the foot of the scarps and counterscarps, bristled with strong fraises, which served instead of revetements, the besiegers had no hope of succeeding by a coup-de-main, and were therefore obliged to proceed by a regular attack. How analogous was this condition of the lines of defence to that of southern Sebastopol after the besiegers had allowed the garrison to recover from their first alarm, and under the guidance of able engineers to place their old works in order, and to supply their deficiencies by new works.

From this description of the defences of Dantzic, it is easy to perceive that the difficulties attending the operation must have been very great. The principal of these, as stated by General Kirgener,¹ who, until the arrival of General Chasseloup, directed the attack, were, 1st, that Marshal Lefebvre had at first an army inferior to that of Marshal Kalkreuth, and that this army was in a great measure composed of new troops, all those destined for the siege not having then arrived; 2dly, that, owing to the badness of the roads and the inclemency of the season, the artillery experienced the greatest difficulty in bringing up its convoys, whilst the establishment of the batteries was retarded, and a scarcity of ammunition sometimes prevailed; 3dly, that the place requiring an immense circumvallation, which, in fact, could not be completed until after the arrival of reinforcements, the corps of troops which occupied the quarters were extremely weak, and hence could neither furnish a sufficient number of workmen at a time, nor even the number of men necessary for guarding the trenches; and, 4thly, that the besiegers had no good plan of the place, no idea of the depth of the ditches, and that, as the accidents of ground in front of the fortifications were extremely diversified, they could only be reconnoitred in proportion as the works advanced. These circumstances, all of which were reproduced at Sebastopol, the necessity of concentrating the greater part of the troops close to the camp of Neufahrwasser, by which succours arriving by sea might debouch, and, lastly, the advantage which the besieged had been able to preserve of remaining masters of part of the suburbs, determined the chief engineer, after the investment had been effected, to direct the principal attack against the Hagelsberg, and a false one against the Bischopsberg fort. The true point of attack was the long branch of lines in the plain connected with the bastion on the right of the Hagelsberg: "c'était là le défaut de la cuirasse;" but, for the reasons above stated, General Kirgener was induced to direct his approaches against the fort itself.

As the details of this great siege would fill a considerable volume, all that our limits permit us to attempt is merely to indicate the principal occurrences. On the 1st of February 1807 the troops of General Dombrowski began to approach Dantzic, and took up a position at Mewe, upon the left bank of the Vistula. On the 15th General Ménard, commanding the Baden contingent, arrived at the same point, and repulsed a detachment of the garrison of Dantzic, which had advanced from Dirschau to attack him. On the 23d General Dombrowski, having been reinforced,

¹ This officer, the head of the engineer staff, and one of the most distinguished in that branch of the service, fell on the field of battle at Bautzen, where he received his death-wound from the same ball which killed Duroc, the grand marshal of the palace, and the intimate friend of Napoleon.

received orders to attack a large detachment of the enemy which occupied an advantageous position at Dirschau and its environs. The combat here was obstinate and sanguinary; but the Prussians, though intrenched in a church and a churchyard, were dislodged and driven back, chiefly by the Poles, who, exasperated by their long resistance, put to death without mercy all who fell into their hands. After the combat of Dirschau, General Munstein no longer sought to obstruct the distant approaches. The troops destined to form the besieging army now arrived in succession, and the park of artillery began to be formed. On the 12th of March Marshal Lefebvre found himself in a condition to close in on the place; and the troops of the garrison having withdrawn, he distributed his own in the following positions: A battalion of French light infantry at Olra, a Saxon battalion at St. Halbrecht in the Burgerfeld, and two others at Tiefensee and Kemplade; the Poles occupied Schonfeld, Kowald, and Zunkendin; some battalions took post at Wonnenberg, Neukau, Schudelkau, and Snickau; the Saxon cuirassiers and light horse were stationed at St. Halbrecht and Guirsekens; the 19th regiment of French chasseurs at Burgfeld, and the 23d at Schudelkau; the Baden dragoons and hussars at Wonnenberg, and the Polish lancers at Langenfurt. On the 16th the marshal attacked the village of Stolzenberg, which he carried after a warm resistance, as he did also the suburb of Schidlitz, to which the Prussians had retired; and on the 18th the place was entirely invested, with the exception of the eastern part, which, by the isle of Nehrung, communicated with Königsberg. Field-marshal Kalkreuth now arrived in Dantzic, and assumed the command of the place. The next operation of the besiegers was the attack of the isle of Nehrung, which, after a severe and protracted struggle, was carried in the most gallant manner, and measures immediately taken to secure possession of this important conquest. A bridge was also established on the Vistula, and various works constructed to check the attempts of the enemy either on the side of Dantzic or on that of Pillau. At this time the governor, who, besides the burgher militia, had under his command a garrison of 18,000 men, made a sortie for the purpose of destroying the works already commenced by the besiegers; but the attempt failed, and the Prussian columns were compelled to retreat to the place without having obtained the smallest success upon any point.

As it had been decided that the principal attack should be directed against the fort of Hagelsberg, favoured by two false attacks, the one directed against the intrenched camp at Neufahrwasser, and the other against Bischopsberg, and also by two other secondary attacks on the left bank of the river, ground was broken on the night of the 1st and 2d April, at the distance of 1600 yards from the pallisades. The approaches were pushed forward with the greatest vigour, and on the night of the 11th the second parallel was commenced by means of the flying sap. On the morning of the 12th the marshal ordered the batteries to be armed, which was accordingly done. On the 13th the enemy made a sortie in force, attacked the Saxons with great impetuosity, carried a redoubt constructed upon the mamelon of Hagelsberg, and even penetrated to the head of the trenches; but they were ultimately repulsed, though not without difficulty and loss. By the 23d all the batteries of the first and second parallels, and those of Stolzenberg, were armed, and emplacements were provided for field howitzers, in order to throw shells into all quarters of the city. At daybreak on the 24th the batteries were unmasked, and though the garrison returned the fire with the greatest vivacity, that of the besiegers soon obtained the ascendancy, committing great ravages in the place. Being apprised of this circumstance, Marshal Lefebvre summoned the governor, who replied in a manner worthy of himself. The fire of the mortar and reverse batteries continued during

the 25th, in the course of which a new battery was constructed between the low flanks of the Stolzenberg; and the direction of some others changed, in order to batter the right bastion of Bischopsberg, the fire of which had greatly incommoded the French batteries. During the day of the 26th, the fire on both sides was exceedingly animated; but at seven in the evening, that of the garrison suddenly ceased, and a column of 600 Prussian grenadiers, followed by 200 workmen, soon afterwards sallied out of the place. As the sortie had been foreseen, however, preparations were made to repulse it, which was done by a combined attack in front and on both flanks, in consequence of which the whole column was either killed or taken. Meanwhile the works were vigorously pushed forward at all points. The batteries of Stolzenberg were united with the attack on the Bischopsberg; emplacements were prepared for batteries à ricochet; at the attack of the Lower Vistula the works were continued, and a tongue of land situated at the extremity of the isle of Holm taken possession of and isolated by means of a cut; whilst at the principal attack the greatest exertions were made to prolong the right of the third parallel, and enlarge the communications. On the 30th April the batteries of the besiegers, augmented by several pieces which had arrived from Warsaw, thundered on the place, in different quarters of which conflagrations now appeared; and the besieged replied by the fire of all the batteries of the front of the attack, directing more than thirty pieces on a redoubt which fired with the greatest effect. But as the fire of the besiegers had made little impression on the exterior fortifications, which were of earth, it was during the first days of May directed chiefly against the palisades, in order to facilitate the assault of the place; and the utmost activity was at the same time evinced in extending, improving, and urging forward the attack; whilst, on the other hand, the garrison showed equal vigour in obstructing the approaches and destroying the works of the besiegers. In fact, notwithstanding the address of the French artillery, that of the garrison still remained effective, because it had not been possible to ricochet the lines of the fortifications, and the resources of the besieged in munitions of all kinds were more considerable than those of the besiegers. In the whole of these circumstances may be seen a rehearsal, as it were, of those of Sebastopol; and the reader will, after a perusal of this description, cease to imagine that the Russians had acquired their knowledge of the use and importance of earth-works from the writings of any author of our day. At Dantzic, as at Sebastopol, a powerful army, guided by a skilful engineer, was enabled to apply the resources of parapet fortification so effectually in defence as to battle for a long time the efforts of the besiegers.

On the urgent recommendation of General Chasseloup, who had by this time assumed the direction of the attack, it was now decided that the isle of Holm should be assaulted, as the possession of it would enable the besiegers to construct new batteries, to take in reverse the front of the attack. The besieged had spared no pains for the preservation of this important post. In the night of the 6th and 7th of May, however, it was attacked, and, after a desperate resistance, carried; whilst the possession of it was secured by works added to the intrenchments which had just been stormed, and the batteries were turned against the place. At the principal attack the fire of the besiegers had also mastered that of the besieged; and Marshal Lefebvre was preparing to assault the fort of Hagelsberg, when a Russian corps d'armée under the command of General Kamenskoi arrived by sea, and disembarked at the intrenched camp of Neufahrwasser.

At the moment of landing his troops, General Kamenskoi was ignorant of the capture of the isle of Holm, and he was disconcerted to find such an obstacle to his communications with the place. This occasioned delay, which

Fortification. proved fatal to his enterprise; for had he attacked immediately on landing, it is not improbable that he would have succeeded. It was only on the 15th of May, however, being the fourth day after the disembarkation, that he resolved to make an attempt to succour the besieged city. He began to debouch at four in the morning, and, under cover of a brisk cannonade, formed his force, consisting of from 11,000 to 12,000 men, in four columns of attack. The onset was impetuous, and at first the Russians gained ground, thrice attempting to penetrate the French line; but they were ultimately repulsed at all points, and forced to retreat with great loss to the intrenched camp. Field-marshal Kalkreuth made no attempt to second this attack by means of a general sortie, which would have placed the French between two fires; and by its failure the fate of Dantzic was decided. Such was the issue of the only effort made by the allies to relieve this important fortress.

The works of the besiegers were now pushed forward with redoubled vigour; and in the course of the following day preparations were made for the assault of Hagelsberg. Foreseeing this, Marshal Kalkreuth resolved to make a last effort to destroy the nearest works of the besiegers, and for this purpose ordered a grand sortie, which took place on the evening of the 20th May; but although the Prussians fought with all the fury of despair, they were at length driven back, and pursued even into the ditch of the place. On the 21st the army of siege was reinforced by the arrival of the troops of Marshal Mortier, part of which had remained before Colberg; the marshal himself quickly followed; and orders were immediately issued for the assault of Hagelsberg. Before giving the signal, however, Marshal Lefebvre again summoned the governor of Dantzic, who, having no longer any hope of being succoured, and convinced that the besiegers were in a condition to make themselves masters of the fort of Hagelsberg, showed a disposition to capitulate. A suspension of arms was accordingly agreed to, and this was followed, on the 24th of May, by a capitulation, the principal conditions of which were similar to those which the field-marshal himself had granted to the garrison of Mayence in 1793.¹

The preceding narrative will in so many respects appear to be an anticipation of the defence of Sebastopol, that it may be well to remark that such as the two defences have been in their beginning and progress so may it be expected that the two sieges will be in their termination—namely, successful for the besiegers. The Prussians and the Russians did everything which bravery and skill could do to save Dantzic, making at the last a bold and gallant attempt to raise the siege by a general attack. Already the Russians have made several grand sorties, and two general attacks of no ordinary magnitude and importance, and it may be expected that before winter they will again endeavour to force the position of the allies; but should they fail, and can it be doubted that they will, how can the Emperor of Russia expect to keep longer from their grasp the just reward of gallantry and perseverance, almost beyond example, for which they have been contending! The hope of the Russians can now only be formed on success in the field, and as that hope becomes with each successive attempt and failure less bright, so must the gloom of disappointment and despair darken until the end shall come, and Sebastopol, although perhaps in ruins, be abandoned to its fate.

BASTIONED SYSTEMS OF THE NETHERLANDS.

The bastioned system of the Italians was soon carried

into other countries by their engineers, who were extensively engaged in the service of foreign princes, and it was thus that the celebrated Italian engineer Marchi, coming to Brussels with Margaret of Austria in 1559, appears to have introduced the bastioned system into the Netherlands. It has been shown that in rampart defences, the ordinary earthen scarp adopted in ditches of parapet works had been replaced by a masonry revêtement as a security against surprise, in consequence of which, in old Italian fortresses, lofty revêtements were almost universal; but in a country the soil of which was permeated by water within a few feet of the surface, such a mode of guarding against escalade would have been enormously expensive, and in consequence advantage was taken of the nature of the country to form broad wet ditches round the ramparts, and thus, by securing them from any sudden attack, to render the revêtement unnecessary. The first example of a fortress surrounded by simple earthen ramparts without revêtements is said to be that of Breda, fortified in 1553 by Count Henry of Nassau, and this arrangement required only to be moulded into the bastioned trace to constitute the ancient system of the Netherlands, as described by Freitag in 1630. Freitag made the flanks of his bastions perpendicular to the curtain, the faces 98 yards long, with a flanked angle not exceeding 90°, and the length of the curtain 149 yards.

Freitag had strange notions respecting his profiles, regulating the height and thickness of his ramparts not so much by the resistance they were required to make against artillery as by the number of sides of his polygon; but disregarding these vagaries of the systematist, the annexed cut, fig. 40, may be assumed to represent the profile usually adopted by the Dutch engineers, R being the body of the place, F the fausse-braye, D the ditch.

Fig. 40.

It will be observed from the profile, that the main rampart is surrounded by an advanced parapet called a fausse-braye, a work to which reference has been made in a preceding page. By this parapet it was intended to obtain a grazing fire on the ditch, whilst the space between it and the rampart formed a spacious chemin des rondes well fitted for the assemblage and movement of troops for defensive purposes; but great as these advantages are, the fausse-braye has dropped into disuse, as it was found scarcely possible to remain in it under a heavy vertical fire, the shells either dropping directly, or rolling down into it from the superior slope of the rampart above. Such shell traps, as they are called, are scrupulously avoided by modern engineers, who well know that the improvement of vertical fire will ere long add materially to the difficulties of defence. In the recent bombardment of Sweborg, a tolerable illustration has been afforded of what may be done by heavy mortars, when the shell has been made a better representative of a mine than it now is. At present a 13-inch shell weighs, when loaded, 200 pounds, and may carry with it, when filled, a charge of 11 lb. of powder, which is ample for breaking the shell and scattering its fragments, but is insufficient for producing great effects as a mine. Should however the projects of Nasmyth and of Mallett be carried into effect, and there can be little doubt that in a modified shape and degree they will, the shell becoming a mine will

¹ Dumas, Précis des Evénemens Militaires, tom. xviii., chap. 19, p. 123. Relation authentique du Siège de Dantzick. "Les principales conditions de la capitulation furent que la garnison portait avec armes et bagages, drapeaux déployés, tambour battant, mèche allumée, avec deux pièces d'artillerie légère et leur caissons attelés de six chevaux, pour être conduite aux avant-postes de l'armée Prussienne à Pillau, en passant par l'île de Nehrung, et en cinq jours de marche. Cette garnison s'engageait à ne pas servir contre l'armée Française pendant un an." (Dumas, ubi supra.)

Fortification. carry with it 1, 2, or 3 cwt. of powder, to destroy not only buildings, but also earthen parapets and ramparts. Passing from the ancient Dutch system as described by Freitag, Marolois, and others, the modern or improved Dutch system of Coehorn deserves especial attention, and is represented in Plate CCLXI, fig. 1, which exhibits his first system.

The great characteristic in this system is the combination of wet and dry ditches, and the use of covering works, or couve-faces, intended to preserve the body of the place

from injury till an advanced period of the siege. These Fortification. envelopes were first proposed by Dürer, and in like manner the remarkable orillon of Coehorn is a reproduction on a moderate scale of the complicated masonry, or casemated structure of one of his bastions. Coehorn was also well acquainted with the principles enunciated, and the systems proposed by the truly eminent German engineer Speckle, and has manifestly adopted them when applicable to his purpose. The profile, fig. 41, will best enable the student to appreciate the difference between the dry ditches of

Fig. 41.

Coehorn and the narrow passage afforded by the fausse-braye of the older engineers. A, inner or upper bastion; B, outer or lower bastion; D¹, dry ditch betwixt the two; D², wet ditch.

The profile also exhibits the loop-holed galleries of the counterscarp, by which a reverse musquetry fire may be obtained on the revêted scarp of the inner rampart; a system of defence which has since been very generally adopted, and is most valuable when a secure communication can be kept up between the galleries and the work which they are intended to defend. After the great siege of Corfu by the Turks, and its successful defence by Schullemburg, some Dutch engineers who had been invited to Corfu by him, and had taken part in the defence, were employed in adding detached forts to the old Italian bastioned fronts. In these works, now partly in ruins and partly destroyed, numerous examples of loop-holed galleries and loop-holed traverses may be observed, and they serve to demonstrate, that though Coehorn adopted in his systematic writings his beliefs to the aquatic sites of Holland, he developed principles and means of defence which were equally applicable to other sites and other countries. It has been argued by Bousmard and others, that an opening would be formed by shells through the couve-face; and that the flanks of the bastions would be thereby exposed to the fire of the counterbatteries on the glacis; but it remains yet to be proved whether such an opening through an earthen mass as is here assumed to be made by the horizontal firing of shells could really be thus effected; and the French translator of Zastrow, M. Neuens, captain of artillery, justly remarks, "that if shells fired horizontally into earthen works are so efficacious in destroying them, such shells must be a still more powerful instrument in the hands of the defenders for destroying the besiegers' batteries." If indeed, Zastrow himself observes, we admit with Coehorn and others, that though the besieger may succeed in destroying a few feet of the parapet of the lower or outer face of the bastion, he would in vain by firing horizontal shells into its mass endeavour to lay open the counterscarp galleries, it must be admitted that the besieger on mounting the low face would find himself in a most critical position, as all the defences, both direct and reverse, of the dry ditch, would remain uninjured, and be in full action against him. These dry or inner ditches, as greatly facilitating the war of sorties, and the reverse or counterscarp galleries, are defensive arrangements of great merit, and may, by fitting modification of profile, be adapted to any site; though, of course, the advantage possessed by the dry ditches in such countries as Holland, of not allowing the besieger to excavate in them without

coming to water, cannot be expected in other sites, and must be made up for by stone pavements, or other contrivances likely to embarrass the besieger in his excavation. Coehorn assumes the plane of site to be only 4 feet above the level of the water, and the dry ditch of his bastion is at its centre just on the level of the water, so that a passage by sap becomes impossible, as the spade sinks at once into water; but near the scarp and counterscarp the ditches only sink 2½ feet, sloping on each side towards the central portion. The breadth of the dry ditch of the bastion is 98 feet, and that of the wet ditch before the salient 148 feet. All the slopes are at an angle of 45°. The whole breadth or thickness of the couve-face, measured at the water level, is 52 feet, so as not to allow room for the besiegers' batteries; and its relief of construction only 12½. Ravelin, relief of low face 10 feet, of high face 18½, and the height of its revêtement 8 feet; here also the thickness of the low face would not afford space for forming batteries. The width of the dry ditch is the same as that of the bastion. These few details, together with an examination of the Plate CCLXI, and of the woodcut 41, will enable the student to comprehend the general principles of this great engineer, and it is rather by tracing out the several ideas of a master mind, as exhibited in the peculiarities of his plans, than by studying the plans themselves as wholes, that the younger engineer will acquire that store of practical knowledge which will enable him to vary his own projects, so that they may really be the best suited for the ground he is working upon.

Coehorn himself exemplified the observations which have been here made, as he never restricted himself to the rules even of his own system. In fortifying Gröningen he was required to construct works on an eminence which commanded the town, and he adopted a trace which, towards the exterior, exhibited a series of tenailles, the gorges of which were closed by small bastioned fronts constructed of walls which should be easily breached from the main works when the enemy had succeeded in gaining possession of any one of the intervening redans. By this curious combination of the tenaille and bastioned systems, Coehorn gave an undoubted proof of his superiority to the narrow prejudices which prevent many men from adopting the system best suited for the particular place. His example should be followed by every sensible engineer.

BOUSMARD, CARNOT, CHASSELOUP, DUFOUR, HAXO, CHOUMARIA.

It would be wrong to dismiss the subject of bastioned systems without at least some more reference to the works of

Fortification. these distinguished engineers than has been given in tracing the history of this subject. Bousmard makes the faces of his bastions as well as their flanks curvilinear, the former convex, and the latter concave outwards; but though from this arrangement the effect of ricochet fire may be diminished, the difficulty of effectually defending the salient from the flanks is much increased. His great innovation, however, consisted in placing the ravelin and its redoubt in advance of the glacis of the body of the place, and forming in front of them a second or advanced covered-way; the object of the arrangement being to close the main ditch entirely, so that the batteries should not fire upon the body of the place through the ditch of the ravelin. The covered-way is made en cremaillère, and at each bend there is a sort of redoubt, or casemated traverse, not a simple hollow traverse loop-holed, such as those in the detached works of Corfu. It has been objected to Bousmard's system that his advanced works would be speedily taken by turning the gorges both of the ravelin and its redoubt, but it should be remembered that the interior slope of both is replaced by a loop-holed wall, being the front of an arched gallery running all round, so that the enemy could not remain within exposed to the fire from the galleries, as well as to that from the body of the place. Without advocating the precise form and disposition of the works recommended by Bousmard, it may be reasonably asserted that in every case of a powerful and well appointed garrison the defence will gain by assuming an active character beyond the precincts of the glacis.

It has been already observed that an unmerited indifference has been manifested by many engineers to the merits of Carnot, principally, it may be believed, from his exaggerated estimate of the effects of a vertical fire of small projectiles. Notwithstanding, however, his appeal to imagination rather than to calculation, when he assumed that by substituting 600 wrought iron balls, weighing each $\frac{1}{2}$ lb., for the one shell of 150 lb. he might expect with 6 mortars to project 3600 balls, and to put hors de combat 20 men at each discharge, or in 100 discharges 2000, he was right in urging the importance of vertical fire. Carnot, born in 1753, was at an early age a member of the Corps of Engineers, and for his mathematical works elected a member of several learned societies. At the Revolution he was a member of the constituent Assembly; he voted for the death of the king, distinguished himself in the army of the North, and when a member of the committee of public safety, directed in great measure the movements of the French army. In 1795 he was named minister of war, but quickly expelled by Barras and exiled the country; but being recalled, was again, in 1799, appointed minister of war. In 1802 he retired from office, and with that stern integrity which marked his character and made it resemble so much the noble independence of Arago, he voted against the elevation of Napoleon to the imperial dignity. Napoleon did not allow this rigid adherence to principle to disqualify the patriot for employment, and charged him with the defence of Antwerp, as he at a later day named him a peer of France, and confided to him the office of minister of the interior. After the fall of Napoleon he became a member of the provisional government, and was immediately afterwards banished from France. He died at Magdeburg in 1823.

Carnot constructed his scarp without a revêtement but placed a detached loop-holed wall in front of it with a chemin des rondes between, which is one essential feature of his system, the wall being constructed with arched niches in rear so as to shelter the men defending it; the loop-holes are in two rows. He provided arched casemates for mortars on the gorge of his bastion in order to fire upon the capital, and the loop-holed wall of an inner curtain being continued along the retired flanks and in front of these mor-

Fortification. tar casemates, formed a complete inner retrenchment. Between the tenaille and the ravelin was an elevated earthen cavalier, occupying the position of a redoubt in the ravelin, before the bastion's counterguard; so that the whole of the interior works were masked by these earthen envelopes. There is much ingenuity in these arrangements, and at least as full an appreciation of the value of earthen works as can be found in the writings of any modern writer. Carnot's leading principle however was, that a successful defence must depend on the active operations of the garrison, and that sorties therefore should be frequent and determined as soon as the enemy had approached close to the fortress. For this purpose he removed the revêtement from the counterguard, and formed it into an easy, or countersloping, glacis to admit of the ready advance of the troops from the ditch upon the head of the besiegers' sap. He supposed that the overwhelming vertical fire of the 10 mortars in the mortar batteries in the gorges of his bastions would prevent the enemy from accumulating large covering parties in the trenches, and that he should therefore be able to fall upon the working parties and successfully delay the progress of the works. It has been shown that Carnot entertained an exaggerated view of the effects to be produced by a peculiar description of vertical fire, but the idea of securing his mortars in casemated buildings is good and has been adopted in one part of the citadel of Ghent; and it is impossible to study his works without being benefited by them. Chasseloup was born in 1754, and died in 1835. He was a lieut.-general, and under Napoleon, Lieut.-General of engineers. Like Bousmard he placed his ravelin in advance of the glacis, and provided it with a small casemated keep, the flanks of which are pierced for two guns each. The tenaille is also provided with casemated flanks, and in front of it is a casemated redoubt or bastionette to supply the place of the ordinary ravelin, and to flank the salient portion of the face of the bastion, the general face being by him bent into two so as to place the salient portion in line with the exterior side of the polygon and thereby secure it from the ricochet fire. Casemated redoubts in the re-entering and salient places of arms, a defensive barrack, and a permanent entrenchment on the bastion are also included in his arrangements. De Sellon (Memorial de l'Ingénieur Militaire) observes, "It would indeed be well to force the besieger to pass through two sieges, if the outworks, pushed so far forward, had higher scarps, and were not so easily turned at the gorge; but as the scarp is only 13 feet high, this possibility of attacking the works by the gorge without a previous descent into the ditch, presents such serious inconveniences that it is surprising to observe that Bousmard and Chasseloup should have adopted so defective an arrangement." But notwithstanding this strong condemnation, it is at least doubtful whether such works are not the most suitable for a vigorous defence by a strong garrison, as they would enable the besieged to fall upon the assailants at the most critical moment of their attack with a powerful force; and further, it may be added, that a skilful engineer would know how to throw many difficulties in the way of turning these advanced works, whilst the continuance of the besiegers in them might be rendered both difficult and dangerous in the extreme.

The most remarkable feature in Dufour's modification of Dufour, the modern system is, that one face of the redoubt in the re-entering place of arms is carried across the ditch, and connected with the coupure of the ravelin, so as completely to close the ditch and cover the face of the bastion from the fire of a battery on the glacis of the salient of the ravelin. Dufour also raised the salient of the ravelin into a high cavalier, so as to secure the faces from ricochet; and he proposes that the cavalier shall be formed of gravel or small stones, so that the fire from the body of the place may cause the enemy, when he has in part destroyed it, and is

attempting to form a lodgment, great damage by scattering about these natural missiles.

General Noizet has been already mentioned in connection with the modern system, his modification of which is now the normal system adopted at all the French military schools. Not adopting Dufour's mode of closing the ditch of the ravelin by carrying across it one face of the redoubt of the re-entering place of arms, he effected this object by placing a massive mask between the coupure of the ravelin and the re-entering place of arms, from the inner scarp of which it is separated by a passage. The counterscarp of the bastion is carried continuously along the inner edge of the mask, whilst in front of it is a ditch which separates it from a demi-caponnière forming its counterscarp and covered-way, and a glacis sloping down the ravelin of the ditch. The mask, the lunette redoubt in the ravelin, and the redoubt in the re-entering place of arms, form a combined series of works of great efficiency for defence, and which completely cover all but the salient portion of the face of the bastion. The flank of the bastion, as before observed, forms an angle of 80° with the line of defence, and the advantage taken of this in the citadel of Ghent in forming a most powerful intrenchment in the bastion, with a curtain as long as that of the main front, has also been pointed out.

General Haxo was one of the most able engineers of modern times. Under Napoleon he distinguished himself at the sieges of Lerida, Mequinenza, and Tarragona. On the restoration he was appointed president of the engineer committee, and directed the construction of the fortifications of Belfort, Sedan, Grenoble, and l'Ecluse. He directed the operations of the siege of Antwerp, and died in 1838. Haxo did not publish his scheme of defence, nor did he reproduce it as a whole in the works he constructed; doubtless considering, as has been so frequently urged, that systems, so called, can only be looked upon as the exhibition of great principles, not as a rigid rule for their application. His ravelin is made very prominent, and the salient is formed into a traverse, or mask, casemated and armed with artillery. Within the ravelin there is a redoubt, and within that a casemated caponnière or bastionette. The ditch of the ravelin is closed by continuing the counterscarp across it with a glacis slope into the ravelin ditch, and by this arrangement the ditch of the redoubt in the ravelin is also closed. The counterguards, the higher and the lower bastions, form almost three lines of defence, of which two, the outer and inner, are powerfully armed with artillery. The peculiar characteristic of the system is, that the parapet is thrown back, and made in its trace independent of the scarp, so that, whilst the latter retains the usual straight line, the parapet is broken into several portions not in the same line, and thus secured from the effects of ricochet—an arrangement of very great merit. Haxo is probably better known to English engineers as the inventor of casemated batteries à l'Haxo than from his merits as an engineer, great as they manifestly were. These batteries are formed in the parapet, and though arched over with masonry are covered with earth. They are open in the rear to the terreplein, and the openings in front for the guns are continued into embrasures formed in an extension of the parapet at these points beyond its ordinary retired position in Haxo's system. These batteries are thus secured from the effects of the enemy's fire, and when the embrasures are masked are equally hidden from his view, so that they may at any moment suddenly open a powerful and unexpected fire upon the besiegers. Being open in the rear, and connected together by arched openings between every pair, the circulation of air is sufficient to do away with the inconvenience from smoke, so generally complained of in casemated batteries. The batteries à l'Haxo have been used at Grenoble and Lyons, and in the forts of Loyasse and Sainte-Foy.

The work of the commandant of engineers, M. Choumara, entitled Mémoires sur la Fortification, was published in 1847. In this work he maintains the principle, that the direction of the parapet should be independent of that of the scarp, the latter being formed in straight lines, and considered permanent during the siege, whilst the former may be broken into several lines, and may be modified during the siege so as to facilitate the defence in any direction. Haxo had in his lessons or studies pointed out the importance of this principle; but Choumara was the first to advocate it in print, though it should be observed that the castle of Naples exhibits an early example of the reverse operation, a new scarp having been built in front of the ancient round-tower forts, so as to change them at the base only into bastions, whilst the upper portion of the towers became retired and independent parapets. Choumara, not relying on the bent trace of his retired parapet as a security from ricochet, proposed a traverse in the capital of his bastion, placed outside of the retired parapet, and 33 yards in length. This traverse, made 26 feet high and 78 feet wide at its base, would occupy less than two-thirds of the space of the twelve ordinary traverses required to secure from enfilade the faces of Choumara's bastions 164 yards in length, whilst it would cover not only the bastions but also the flanks. In addition, however, to the traverse or mask in the capital, Choumara proposed high traverses, formed parallel to the flanks, at about 22 yards from the salients, which would not only secure the faces from enfilade, but would form secure or interior flanks, as cavalier flanks commanding and firing over those in front. By making the cavalier flanks 98 yards long, and casemating them à l'Haxo, 15 guns might be placed in each, and the covered-way of the bastion attacked would be commanded by 30 guns in addition to those of the ordinary flanks, whilst the traverse of the capital would secure the flank cavaliers from ricochet. Any one who reads and studies these simple and yet effective arrangements will not, it is hoped, longer imagine that the importance of earthen works in their proper place had been overlooked by modern engineers, even though they had learnt to value the beautiful and scientific arrangements of their predecessors. The last and most remarkable suggestion of Choumara is another illustration of the same remark, as he proposes to widen his ditch to about 50 yards, and leaving a passage of communication of 16 yards round the base of the scarp, to form an interior glacis, sloping up from the base of the counterscarp towards the summit of the scarp, and having a base of 34 yards wide, thus constituting a continuous mask round the whole escarp. In respect to countermines, Choumara proposes to replace the great galleries, which are usually made 6 feet high and 3 feet wide, and which are, as it were, the great arteries of a system of mines, by large vaulted galleries from 16 to 20 feet wide, pierced through the counterscarp, and continued as far as the third parallel. Six of these galleries were to be formed in each front, being placed about 55 yards apart, and connected together by minor transverse galleries or branches. Galleries of this magnitude would, in time of peace, be useful as stores, and in time of war would greatly facilitate the operations of the miner. The subject of military mining is so extensive in itself, that it must be deferred to a future article on the subject; but it may be here stated, that this subterranean warfare exercises great ingenuity, and requires great skill both on the part of the besieged and the besieger. The besieger has had the advantage of forming the main galleries of his countermines beforehand, but in spite of this a war of mines must generally be in favour of a besieger, since every explosion of the mines of the besieged, however partially destructive it may have proved to the immediate assailants, must destroy some portion of the works of defence, whilst each one of the besieger's mines must operate in favour of the attack alone. Starting,

Fortification. however, with this principle, that a fortress, except in some situation which renders regular attack impossible, must ultimately fall, the real object of defence is to occupy the enemy for a sufficient time to suit the purposes for which it was constructed, and in this view of the case the destruction of the battery or of the lodgement of a besieger might materially protract the resistance of the intrenchment formed in a bastion, and thus enable the besieger to maintain his ground so much the longer. The most simple form of mine, and that which may be most readily applied as an obstacle in the way of the assailant, is the fougasse. It consists of a chamber placed at the bottom of a simple pit about 12 feet deep, so as to dispense with the labour of forming a gallery. The charge is placed in a wooden box, and both the charge and size of the box may be thus estimated. When the line of least resistance, or shortest line drawn from the centre of the charge to the surface of the earth, which in this case is the depth of the pit, is 10 feet, a charge of 100 lb. will produce an entonnoir or excavation, the radius of which is equal to the line of least resistance, and it has been ascertained that the volume of the excavation varies with the charge, the line of resistance and the resisting medium being the same, and that the volume varies also as the cubes of the lines of least resistance; hence, therefore, if $W$ represent the weight of the charge, $B$ the bulk of the entonnoir corresponding to 100 lb. of powder and a line of resistance equal to 10 feet, and $b$ that of the entonnoir corresponding to the charge $W$ and the line of least resistance $R$ , we have $100 : W :: B : b$ ; but as $B : b :: 10^3$ :

$R^3$ , we have $100 : W :: 10^3 : R^3$ , and $W = \frac{R^3}{10^3}$ . Now let $S$

= side of cubical box to contain the charge—55 lb. of powder thrown loosely in filling one cubic foot, and $S =$

$\sqrt[3]{\frac{R^3}{10 \times 55}} = 0.122 R$ , or nearly $\frac{1}{8} R$ in feet. The pits

for fougasses vary generally from 8 to 12 feet in depth, and from 3 to 4 feet in width, being made square, and either secured by being revetted with planks or not, as the earth is or is not firm enough to support itself; and for this latter purpose gabions may be used made of different diameters, so that one may be slipped through the others which have been previously fixed. The box for the powder is well tarred, and when intended to be left in the ground for some time, it may be covered with tarred canvas and then put into another box, also tarred both inside and out. The charge is ignited by a saucisson or linen tube about an inch in diameter, filled with powder, and either laid in a wooden case well tarred, or suspended in it. The saucisson and its wooden case, or other covering, whatever it may be, should be sunk some feet in the earth in conveying it from the charge and pit to the place from which it is to be ignited, in order to secure it from accidents as well as from the enemy's observation (see woodcut, fig. 41). In the figure is also represented the mode in which the fire is applied by what may be called the fire-box, the end of the trough and powder-hose being introduced into it. As the object of military mines requires immediate explosion, it is manifest that the firing must be effected by some contrivance for producing instantaneous ignition to be really effective, but this may now be done in so many ways independently of voltaic action—by the use, for example, of friction and detonating tubes—that it would be useless to detail them. It is true that experience has shown how little real injury the explosion of fougasses can do to an assailant; but, as the moral effect of the belief of their existence is a certain degree of hesitation or irresolution, often greater than that produced by actual casualties from musketry fire, the mine must still be considered useful to defence as an obstacle in the way of the assailant. Loaded shells packed in a case may be substituted for the ordinary

charge, the case being formed with a partition, and the fougasses of the shells placed on the lower portion of the case, passing through holes in the partition, so as to be brought into connection with the saucisson or firing-hose in the upper portion of the case. Another form is the stone fougasse, which is probably the most effectual of all. It is constructed thus: a conical pit is made in the earth about 5 or 6 feet deep, the axis being directed towards the enemy at an angle of $45^\circ$ with the plane of construction, and at the bottom a charge of 50 lb. of powder is placed in a well-tarred box. Over the box, and perpendicularly to the axis of the cone, is fixed a lid, on which as a platform are packed either stones or broken bricks, which, on explosion, are scattered over a space of about 60 by 70 yards. It should be laid down as a rule that means for discharging mines ought to be provided within the fortress, either by using the voltaic battery for the purpose, or by preparing openings in the works through which the powder-hose may be carried.

The last great modification proposed by Choumara is the extension of the exterior side, and this can no longer be a matter of doubtful expediency when the effective range of the rifled musket has become equal to that of smaller ordnance. The length of the line of defence may now be safely and advantageously fixed at 400 yards, so that musketry and artillery may co-operate together efficiently. Chasseloup had, indeed, also proposed to make his exterior side about 700 yards long; and he was not a mere speculative engineer, as he had fortified with great skill under the orders of Napoleon, Alessandria in Piedmont; but it must be borne in mind that no greater distance should be allowed for musketry than is compatible with distinct vision and a correct appreciation of distance, and further, that the men intended to use the rifle in a fortress ought to be well trained for that object, as the loose fire of untrained men would probably be little better with the rifle than with an ordinary musket.

CONCLUSION.—GERMAN SYSTEMS OF DEFENCE.

After having traced the history of bastioned defence to the high state of perfection it has now attained, a brief summary of other systems seems necessary to complete the subject. It has been shown that no sooner had the Italians invented the bastioned system of defence, than it found in every country persons who devoted themselves to what they considered the improvement of its details: France had its Errard, its Pagan, and its Vauban; the Netherlands its Freitag and its Coehorn; Germany its Speckle; and it may be asserted that the last-named was at least equal to any of the others. Germany, however, though it might have justly prided itself on Speckle, has gone back to Dürer, and adopted from him the other system of flanking defence, which depends on the use of casemated galleries, and of caponnières or casemated works thrown across the ditches. Yet though this has become the result, it is remarkable that the Germans have taken their systems, as exhibited in the most remarkable of their modern works, from a French officer—the celebrated Marc René, Marquis de Montalembert, who was born in 1713, and commenced his military service as an officer of dragoons in 1731. He was a person of very varied acquirements, and became when still a youth a member of the Academy of Sciences of Paris, but fortification and the art of war were his favourite studies. In 1776 he published his celebrated work entitled "Perpendicular Fortification, or an Essay on Several Methods of Fortifying a straight line, a triangle, a square, and all polygons of any number of sides, giving to their defence a perpendicular direction. Also, Methods of Improving Existing Defences, and rendering them much stronger. Also, Redoubts, Forts, and Field Intrenchments, of a New Construction," a colossal work, embracing 11 quarto volumes, enriched with 165 large plates, and which must be considered the source from

which all the modern inventions in this branch of fortification have been derived. In referring back to earlier German writers, it appears that Rimpler in 1673 proposed a system which is a combination of bastions with tenailles, and Landsberg one in 1712 which is purely a tenaille system; but both of these adhere to earthen ramparts and parapets, either with revêtements in the first, or without them in the second, and their systems may be therefore considered an extension of the trace of parapet fortification to rampart fortification. But Montalembert, in his tenaille system, replaces the simple revêtement at the re-entering angles with casemated works in two stages, thus affording both direct artillery and musketry for the defence of the ditch and faces of the redans, the remaining portion of the trace being occupied by an earthen couvre-face work, with a detached loop-holed gallery in front of it, being evidently the prototype of Carnot's detached revêtement. The re-entering casemates were calculated to hold 24 guns in two tiers. Behind the couvre-face was the body of the place of the redan, being also fronted by a casemated gallery, and separated from the couvre-face by an inner wet-ditch. In this system, then, the defence by musketry as well as by artillery is at two levels, the one at a moderate height above the bottom of the ditch, and not, as in the old Italian systems, at the high level of the crest of the parapet. At the gorge of each redan is placed a formidable casemated tower; whilst in front of the main ditch there is a general couvre-face provided also with casemated galleries, a second or advanced ditch, places of arms in front of the re-entering angles, a covered-way, and a glacis.

The polygonal system may be considered as springing directly from Dürer's work of the same name, only in this case the simple earthen ramparts of Dürer are exchanged for a combination of casemated towers, casemated galleries, earthen couvre-faces; and the caponnières, which, as in Dürer's, flank the ditches, assume the more artistic form of bastionettes. In Dürer's polygon the sides were straight or unbroken, but in Montalembert's the centre was thrown back and formed into an Italian bastioned trace, the faces flanking the faces of the caponnière, and again, therefore, exemplifying the difficulty of ensuring perfect flanking defence by any other trace. In forts which formed a triangle or square Montalembert was rich in resources, though the massive casemated tower, casemated galleries, and earthen couvre-faces may be considered the essential elements of all. In France, the views of Montalembert have never been received with enthusiasm, though Cherbourg is fortified in conformity to them, and it was even alleged that the corps du génie was indisposed to receive instruction from an officer of another arm; but it is more reasonable to suppose that the cherished name of Vauban has induced its officers rather to direct their attention to the improvement of the bastioned system, which they have certainly carried to perfection, than to the development of one depending on such different principles. In Germany, on the contrary, Speckle is less known than Vauban, and though probably a thought of Dürer may not enter into the question, Montalembert's systems, founded upon some of his principles, have been readily adopted, and may be studied in the works of defence of Coblenz. In all such works masonry defences or casemated buildings assume a character of the highest importance, but it should not be forgotten that no masonry can resist the force of a concentrated fire of heavy guns, and can only be considered safe when protected by earthen masks or couvre-faces. The Maximilian towers of the defences of Lintz, therefore, are not now approved by modern engineers, and the Russians have exhibited their distrust of the most formidable looking masonry defences, even when opposed to ships, by closing the harbour of Sebastopol against approach by sinking a large portion of their own fleet; and this is not

to be wondered at, when it is remembered, that to bring the guns forward in order to give them a necessary latitude of fire within casemated batteries, the walls must be much cut into, and therefore greatly weakened. This great defect of masonry defences is well known to engineers, in addition to the further evils of smoke in close casemates, but it is presumed that no one who has read this essay will now imagine that it was necessary to wait to the present epoch for this knowledge, as the earthen mask or couvre-face has been shown to have been applied at a very remote period of the history of the science. In the earliest periods of the Italian fortification, the necessity of increasing the active power of the flanks beyond that which could be obtained by their length alone was strongly felt, and in consequence retired flanks, one rising above the other, were adopted, as well as casemated flanks which admitted of two or more tiers of guns, thus, as in Montalembert's system, obtaining a greater number of guns by extending the battery vertically. At first sight this appears a natural mode of gaining a superiority over the attack, in which the batteries can only be extended laterally, but in practice the retired flanks were soon found to be untenable, as those in front were complete shell-traps, and the casemates were practically useless from the difficulty of clearing them from smoke. The systems of Montalembert partake of the same defects; and however imposing the appearance of several successive tiers of guns may be, it should be remembered, that, if covered by the mask, they can only be partially used when the enemy is at a considerable distance, and that the tiers exposed to view may be easily destroyed by the guns of attack of the calibres now used at 500 yards. Several writers have proposed systems based upon similar principles to those of Montalembert, but it is perhaps sufficient here to mention the work of Don Jose Herrera Garcia (Teoria Analitica de la Fortificacion Permanente), as it unquestionably affords the most remarkable development of the tower system of defence. Garcia proposes several successive lines of massive casemated buildings or towers, of an egg-shape, connected together with what may be called casemated curtains. The towers are surmounted by a parapet, which at the ends next the enemy is broken into a series of smaller curves, and is retired or independent of the exterior wall or scarp. As each of these towers is defensible of itself, the work of forcing a way through three lines of them would undoubtedly be most formidable, but of course the expense of such a system would be enormous.

The system of the Swedish general Virgin belongs to the bastioned systems, but it is mentioned here in contrast to Garcia's, as it disperses in the defences separate bastioned forts of a form somewhat approaching to Rimpler's, and covered by outworks so arranged as to secure the inner works from injury until the enemy has effected his lodgement upon them. These forts were to be surrounded on all sides by ditches, and connected together by secure communications. Ingenious as Virgin's system is, it is manifest that though the loss of one fort would not ensure the fall of the others, it would at least render all the interior space inclosed by the line of forts untenable, and place the town, the arsenal, or other public buildings, at the mercy of the besiegers. This may be said of all detached forts, and it must be again laid down as a maxim, that the ultimate value of such forts, as a means of securing some important object, depends on an inner line of defence of a nature to resist any sudden attack or coup-de-main; and this principle should be applied to the defences of such places as Portsmouth and Gosport. Detached forts will be, for such a purpose, more effectual than a simple continuous line, as they may be so placed as to keep the enemy at a proper distance, but they will cease to be of use if an enemy can safely pass them and attack a defective interior line behind, incapable of resisting a coup-de-main.