AGGER, in ancient military writers, denotes the middle part of a military road, raised into a ridge, with a gentle slope on each side, to make a drain for the water, and keep the way dry. AGGER 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 _aggeres_. Bergier mentions several in the _Gallia Belgica_, which were thus raised 10, 15, or 20 feet above ground, and 5 or 6 leagues long. They are sometimes called _aggeres calceati_, or causeways. AGGER, also, denotes a work of fortification, used both for the defence and the attack of towns, camps, &c. in which sense _agger_ is the same with what was otherwise called _vallum_, and in later times, _agestum_: and among the moderns, _lines_; sometimes, _cavaliers_, _terrasses_, &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 had also a ditch, which served as its chief defence. The height of the _agger_ was frequently equal to that of the wall of the place. Cæsar tells us of one he made, which was 30 feet high, and 330 feet broad. Besides the use of _aggers_ before towns, they generally used to fortify their camps with them; for want of which precaution, divers armies have been surprised and ruined. There were vast _aggers_ made in towns and places on the sea-side, fortified with towers, castles, &c. Those made by Cæsar 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. Besides, the principal _agger_ or _vallum_, on the brink of the ditch, Mr. Horsley describes another on the south side of the former, about 5 paces distant from it, which he calls the south _agger_; and another larger one, on the north side of the ditch, called the north _agger_. This latter he conjectures to have served as a military way; the former, probably, was made for the inner defence, in case the enemy should beat them from any part of the principal _vallum_, or to protect the soldiers against any sudden attack from the provincial Britons. AGGER _Tarquinii_, was a famous fence built by Tarquinius Superbus, on the east side of Rome, to stop the incursions of the Latins, and other enemies, whereby the city might be invested. AGGER is also used for the earth dug out of a ditch or trench, and thrown up on the brink of it: in which sense, the Chevalier Folard thinks the word to be understood, when used in the plural number, since we can hardly suppose they would raise a number of cavaliers, or terrasses.