whole camp was surrounded by a trench (_fossa_), generally nine feet deep and twelve broad, and a rampart (_vallum_) made of the earth that was thrown up (_agger_), with stakes (_valli_) fixed at the top of it. The labour of this work was so divided, that the allies completed the two sides of the camp alongside of which they were stationed, and the two Roman legions the rest.--In describing the Roman camp and its internal arrangements, we have confined ourselves to the information given by Polybius, which, of course, applies only to his age, and to armies constituted like those he witnessed. When the practice of drawing up the army according to cohorts, ascribed to Marius or Caesar [EXERCITUS], had superseded the ancient division into maniples, and the distinction of triarii, &c., the internal arrangements of the camp must have been changed accordingly. In each legion the tribunes divided themselves into three sections of two each, and each section in turn undertook for two months the superintendence of all matters connected with the camp. Out of the twenty maniples of Principes and Triarii in each legion, two were appointed to take charge of the broad passage or street called _Principia_, extending right across the camp in front of the tents of the tribunes. Of the remaining eighteen maniples of Principes and Hastati in each legion, three were assigned by lot to each of the six tribunes, and of these three maniples one in turn rendered each day certain services to the tribune to whom it was specially attached. One maniple was selected each day from the whole legionary force, to keep guard beside the tent of the general. Three sentinels were usually posted at the tents of the quaestor, and of the legati: and by night sentinels kept watch at every maniple, being chosen out of the maniple which they guarded. The Velites mounted guard by day and by night along the whole extent of the vallum: to them also in bodies of ten was committed the charge of the gates, while strong bodies of infantry and cavalry were thrown forward in advance of each gate, to resist any sudden onset, and give timely notice of the approach of the enemy.--_Excubiae_; _excubias agere_; _excubare_; are the general terms used with reference to mounting guard whether by night or by day. _Vigiliae_; _vigilias agere_; _vigilare_; are restricted to night duty: _Excubiae_ and _Vigiliae_ frequently denote not only the service itself, but also the individuals who performed it. _Stationes_ is used specially to denote the advanced posts thrown forward in front of the gates. _Custodes_ or _Custodiae_ the parties who watched the gates themselves, _Praesidia_ the sentinels on the ramparts, but all these words are employed in many other significations also. The duty of going the rounds (_Vigilias circuire s. circumire_) was committed to the Equites, and for this purpose each legion supplied daily four, picked out from each turma in rotation by the commander of the troop.