Caesar, on learning these proceedings from the deserters and captives, adopted the following system of fortification; he dug a trench twenty feet deep, with perpendicular sides, in such a manner that the base of this trench should extend so far as the edges were apart at the top.
Quibus rebus cognitis ex perfugis et captivis, Caesar haec genera munitionis instituit. Fossam pedum viginti directis lateribus duxit, ut eius fossae solum tantundem pateret quantum summae fossae labra distarent.
He raised all his other works at a distance of four hundred feet from that ditch; [he did] that with this intention, lest (since he necessarily embraced so extensive an area, and the whole works could not be easily surrounded by a line of soldiers) a large number of the enemy should suddenly, or by night, sally against the fortifications; or lest they should by day cast weapons against our men while occupied with the works.
Reliquas omnes munitiones ab ea fossa pedes quadringentos reduxit, [id] hoc consilio, quoniam tantum esset necessario spatium complexus, nec facile totum corpus corona militum cingeretur, ne de improviso aut noctu ad munitiones hostium multitudo advolaret aut interdiu tela in nostros operi destinatos conicere possent.
Having left this interval, he drew two trenches fifteen feet broad, and of the same depth; the innermost of them, being in low and level ground, he filled with water conveyed from the river.
Hoc intermisso spatio duas fossas quindecim pedes latas, eadem altitudine perduxit, quarum interiorem campestribus ac demissis locis aqua ex flumine derivata complevit.
Behind these he raised a rampart and wall twelve feet high; to this he added a parapet and battlements, with large stakes cut like stags' horns, projecting from the junction of the parapet and battlements, to prevent the enemy from scaling it, and surrounded the entire work with turrets, which were eighty feet distant from one another.
Post eas aggerem ac vallum duodecim pedum exstruxit. Huic loricam pinnasque adiecit grandibus cervis eminentibus ad commissuras pluteorum atque aggeris, qui ascensum hostium tardarent, et turres toto opere circumdedit, quae pedes LXXX inter se distarent.