Legion command group: Legatus on foot, Aquilifer, Imagifer, Centurion, plus two slaves
A Roman legion (from Latin legio “military levy, conscription”, from legere “to choose”) was the largest unit of the Imperial Roman army involving over 5200 roman citizens, consisting of centuries as the basic units. Until the middle of the first century, 10 cohorts (about 5,000 men) made up a Roman Legion. This was later changed to nine cohorts of standard size (with 6 centuries at 80 men each) and one cohort, the first cohort, of double strength (5 double-strength centuries with 160 men each). Legions also included a small ala or cavalry unit.
For most of the Roman Imperial period, the legions formed the Roman army’s elite heavy infantry, recruited exclusively from Roman citizens, while the remainder of the army consisted of auxiliaries, who provided additional infantry and the vast majority of the Roman army’s cavalry. (Provincials who aspired to citizenship gained it when honourably discharged from the auxiliaries).
Many of the legions founded before 40 BC were still active until at least the fifth century, notably Legio V Macedonica, which was founded by Augustus in 43 BC and was in Egypt in the seventh century during the Islamic conquest of Egypt.