FORT

FORT, in the military art, a small fortified place, environed on all sides with a ditch, rampart, and parapet. Its use is to secure some high ground, or the passage of a river, to make good an advantageous post, to defend the lines and quarters of a siege, and the like. Forts are made of different figures and dimensions, according as the peculiar nature of the ground requires. Some are provided with bastions, others with demi-bastions; some are of a square form, others pentagonal, and others again are stellated, having five or seven angles. A fort differs from a citadel in this, that the latter is built to command some town.

Vitrified Forts. This name has been given to certain remarkable ruins, situated for the most part on the tops of certain hills in the Highlands and northern parts of Scotland. They were first discovered about the year 1778, by Mr Williams, an intelligent mineral surveyor, who published an account of them some time afterwards. These singular structures derive their appellation of vitrified from the circumstance of the stones composing them presenting the appearance of having been melted or fused by means of fire, thus forming a solid mass of a glassy structure, somewhat resembling volcanic lava, or the refuse of a furnace. The single fact of their vitrification is the only characteristic applicable in a general sense to the whole of these forts. In form, size, and situation, they present every variety. Some of them are round or elliptical, whilst others are in the form of squares or parallelograms. In magnitude they vary from a few yards to some eighty or ninety in length, whilst their breadth differs in a proportional degree. The walls, likewise, as might have been expected, vary much in thickness. Some of them are only two or three, and others are about twenty feet in breadth. In height they also differ considerably, having apparently in some instances been twelve feet, and in others not a third of that height. In one or two instances there are a series of walls, two or three in number, enclosing the same area of ground, with a space between each of the walls sufficiently large to admit of active defensive operations on the part of those who occupied the place. Their vitrification is very irregular. Occasionally it does not extend a few feet above the ground on which the fabric stands, nor penetrate beyond the surface, whilst in a few instances it rises to the height of ten or twelve feet, and passes inwards to a considerable extent on both sides. Sometimes only isolated parts of the walls show traces of vitrification, and that too but on one side; in other instances the process appears to have been completed with elaborate care, as the effects of the heat extend externally and internally over the greater part of their surfaces. They are for the most part placed, not upon the highest elevation of the country where they are

situated, but generally in a commanding position; and they are found sometimes upon the sea-shore, and sometimes many miles inland. In general their structure displays nothing like regular masonry; that is, the stones have not been hewn into symmetrical shapes and cemented together, as is the case in the more modern structures of the same country. A few of them have regular causeways leading up to them, and many are furnished with wells, an indispensable requisite for a garrison. Such is a general description of these singular erections, which have for more than half a century excited so much curiosity and interest.

After the discovery of Mr Williams, the ingenuity of the learned was turned to their probable origin, and several theories and conjectures were hazarded by various individuals upon the subject. By one party they were declared to be of volcanic origin, whilst another contended that they were works of art. Of the latter opinion was Mr Williams himself, who not only declared them to be the result of human ingenuity, but speculated upon the manner in which they were constructed. But before adverting to any of the theories which have been advanced, we shall give a description of the most remarkable of these forts, and this, as far as possible, in the language of those individuals by whom they were examined.

Dun MacSniocain, which lies in Argyleshire, is very fully described by Dr Macculloch.¹ "It is situated on a small rocky hill, which forms a kind of island in the plain, of a narrow prolonged shape, and scarped all round, except at one extremity, which affords access to the summit and the fort. The height of this hill or rock above the plain seems to be about forty or fifty feet; and it is, even in the modern military sense, a strong position. It is important to remark, that the rock consists of limestone and slate intermixed, the plain itself being chiefly alluvial, and the nearest hill and rocks being of trap, and of that pudding-stone so well known to all travellers, which also abounds in the vicinity of Oban. That stone is itself formed of fragments of various trap rocks, and is remarkable for its ready fusibility, while the rock on which the fort stands is of an infusible nature. The fort itself is so contrived as to occupy nearly the whole summit, which is about 250 yards long, and consists of three distinct parallelogramic enclosures. The dimensions of these are as follows, as nearly as could be measured by pacing. The outer is about thirty yards long and about twenty-four broad; the next is about thirty-seven, with a similar breadth; and that at the farther extremity is about fifty-six yards in length, but being imperfect, it may formerly have been longer. Besides this, between the first and second works there is a transverse wall which reaches from the one precipitous face to the other, so as, when entire, to have cut off the communication from without to the two inner works. The circumferences of the two inner enclosures make collectively a line of about 260 yards, which, according to the modern military computation for a redoubt, would contain more than 500 men. The external work would dispose of about a hundred more. Hence it is plain that this must have been a military work of some consequence, as capable of holding a large garrison." The doctor goes on to show the eligibility of this place as one of military defence; and observes, that the walls were probably twelve feet thick. He continues, "when it is said that the walls here or elsewhere are vitrified, it must not be supposed that they form a solid mass of glass or slag. That condition is very various in different specimens

throughout Scotland, and if it is here more perfect than in many, it is less so than in some others. To speak more accurately, many of the stones which form the walls are more or less perfectly slagged or scorified; so that while some have been thus changed throughout, the surfaces only of others are affected, while others again, consisting of less fusible materials, are only burnt. A certain proportion has escaped the fire altogether, or has never been exposed to it; and if we may judge from the ruins, this has taken place chiefly towards the upper part of the wall. The general result, however, is, that in some parts the wall forms a solid mass, but of an irregular composition, consisting of scoria, slag, burnt stones, and stones scarcely altered, united together, but with vacant intervals; while in other places it is separable into lumps of various sizes, and into single stones."

The next vitrified fort described by Dr Macculloch is that of Dunadeer.

"The hill of Dunadeer, having an elevation of about 600 feet² from the irregular plain on which it stands, with a steep acclivity all round, has a flat oval summit, which is entirely occupied by the enclosure, so as to form a strong military position. Though much ruined, and consequently obscured, having apparently been used as a quarry for building a more modern castle in the same spot, it is not difficult to trace either the dimensions or the disposition of the original work. The form is a parallelogram, of which one extremity is curved, so as to be nearly semicircular, and its longest side is about fifty-eight yards, the shortest being about twenty-four. The thickness of the wall seems originally to have been eighteen or twenty feet; although, from the state and nature of the ruin, it is impossible to be very accurate in this particular. The highest remaining portion is about six feet above the present surface; and if one foot be added for the increase of soil, and two for the loss which it has sustained at the summit, to be computed from the ruined part at its foot on each side, we shall have eight feet as the probable original altitude.

"The materials of the hill are chiefly grey granite, an infusible rock; but there are scattered in the surrounding plain blocks of a black variety, which, from containing hornblende, is very fusible. To pass over the obviously more modern ruins at this place,³ as not concerning the present question, there are at a certain stage down the hill the well-marked traces of a work which once seems to have encircled the whole. It is a kind of fortification well known to antiquaries as occurring frequently in the ancient British hill forts; and it resembles a modern military field work, as it consists of a single ditch and wall, the latter being formed of loose stones not vitrified. I consider this as part of the original defences, because a similar one is found on Noath.

"The materials in the vitrified wall are, as at Dun MacSniocain, partly roasted without adhesion, and partly vitrified, or glazed or scorified, in a similar manner. It is easy to see that the dark granite forms the vitrified and scorified substances; but, not to enter on the more minute details, which rather concern the chemist and mineralogist than the antiquary, but which are very interesting to them, I shall only further remark, that where stones not capable of vitrification themselves have undergone this change, it has been produced by the alkali of the wood used in the process; whence the glazed surfaces of many unvitrifiable substances.

"Now I remarked that at Dun MacSniocain the ma-