in the ancient military art, a work of fortification, used both for the defence and the attack of towns, camps, &c. In which sense it is the same with what was otherwise called vallum, and in later times agglutinans; and among the moderns lines, sometimes castra, terrae, &c. The agger was usually a bank, or elevation of earth or other matter, bound and supported with timber; having sometimes turrets on the top, wherein the workmen, engineers, and soldiery, were placed. It was also accompanied with a ditch, which served as its chief defence. The usual materials of which it was made were earth, boughs, fascines, stakes, and even trunks of trees, ropes, &c. variously crooked, and interwoven somewhat in the figure of stars; whence they were called stellati axes. Where these were wanting, stones, bricks, tiles, supplied the office: on some occasions, arms, utensils, pack-faddles, were thrown in to fill it up. We even read of aggers formed of the carcases of the slain; sometimes of dead bones mixed with lime; and even with the heads of slaughtered citizens. For want of due binding, or solid materials, aggers have sometimes tumbled down, with infinite mischief to the men. The besiegers used to carry on a work of this kind nearer and nearer towards the place, till at length they reached the very wall. The methods taken, on the other side, to defeat them, were by fire, especially if the agger were of wood; by fapping and undermining, if of earth; and, in some cases, by erecting a counter agger.

The height of the agger was frequently equal to that of the wall of the place. Caesar tells us of one he made, which was 30 feet high and 330 feet broad. Besides the use of aggers before towns, the generals used to fortify their camps with such works; for want of this precaution, armies have often been surprized and ruined.

There were vast aggers made in towns and places on the sea-side, fortified with towers, castles, &c. Those made by Caesar and Pompey at Brundusium, are famous. Sometimes aggers were even built across arms of the sea, lakes, and morasses; as was done by Alexander before Tyre, and by M. Antony and Cassius.—The wall of Severus, in the north of England, may be considered as a grand agger, to which belong several lesser ones. See Severus's Wall.

agger, in ancient writers, likewise denotes the middle part of a military road, raised into a ridge, with a gentle slope on either side, to make a drain for the water, and keep the way dry.

The term is also used for the whole road, or military way. Where highways were to be made in low grounds, as between two hills, the Romans used to raise them above the adjacent land, so as to make them of a level with the hills. These banks they called aggers. Berenger mentions several in Gallia Belgica, which were thus raised ten, fifteen, or twenty feet above ground. They are sometimes also called aggeres calceati; and now generally known by the name chaufées, or causeways.