The LEGIO was composed of infantry, and, though larger, corresponded to our regiment. It was divided into ten cohorts (battalions), each cohort into three maniples (companies), and each maniple into two centuries (platoons). In theory the number in each legion was six thousand, in practice about four thousand. The usual order of battle was to draw up each legion in three lines (acies triplex), the first consisting of four cohorts, the second and third of three each. The defensive armor of the legionary soldier was a helmet of metal or leather, a shield (four feet by two and a half), greaves, and corselets of various material. The outer garment was a woollen blanket, fastened to the shoulders by a buckle. Higher officers wore a long purple cloak. The offensive armor was a short, straight two-edged sword (gladius ), about two feet long, worn by privates on the right side, so as not to interfere with the shield, but on the left side by officers. The javelin (pilum) was a heavy wooden shaft with an iron head, the whole about seven feet long and weighing fully ten pounds. All legionary soldiers were Roman citizens. The auxiliaries were hired or drafted troops, and were always light-armed. The cavalry in Caesar's time was made up of auxiliaries taken from the different provinces.

The officers were: - 1. The IMPERATOR, or commander in chief. 2. The LEGÁTI, or staff officers, varying in number. Caesar had ten. 3. The QUAESTOR, or quartermaster. 4. The TRIBÚNI MILITUM, numbering six in each legion, and assisting 
   the Imperator in his duties. 5. The PRAEFECTI, who held various subordinate commands. 6. The CENTURIÓNES, who were non-commissioned officers, and rose in rank for good service. There were sixty centurions in each legion, six in each cohort, and one in each century. They were promoted from the ranks, but rarely rose above centurion of the first rank. All the officers, except the centurions, came from either senatorial or equestrian families.

The COHORS PRAETORIA was a body of picked troops that acted as body guard to the Imperator.

The STANDARD (signum) of the legion was an eagle with outstretched wings, perched upon a pole.

The Romans when on the march fortified their camp every night. They made it rectangular in shape, and threw up fortifications always in the same way. It was surrounded by a ditch and rampart. The legionary soldiers encamped next to the wall on the inside of the fortifications, thus surrounding the cavalry, the auxiliaries, the general and his staff. The general's tent was called the Praetorium, and the entrance to the camp in front of his tent was called the Praetorian Gate. The opposite entrance was called the Decuman Gate.