The 28 legions counting a total of 5,000 to 6000 men constituted the largest unit of the Roman Army at the time of Emperor Augustus. All legionnaires were without exception Roman citizens who mostly served as heavily armed infantry. A legion consisted of ten cohorts and four cavalry divisions called »turma«. The latter counted 120 men.
A legate called »legatus legionis« commanded a legion, assisted by two deputies: the military tribune »tribunus laticlavus,« who came from the senatorial class, and the camp prefect called »praefectus castrorum.« Five »tribuni angusticlavi,« military tribunes from the equestrian order, served as staff officers. In addition, another 200 men either handled administrative tasks or worked as doctors.
The high-ranking officers also had a substantial number of slaves, wagons and pack animals at their disposal, a group adding about 200 persons and at least 300 riding, draught and pack animals to a legion. All in all, a legion consisted of circa 6,500 men, of whom 5,300 to 5,500 were soldiers.
The legions were given numbers. In Augustean time, numerous legion numbers were assigned twice, because Augustus kept the traditional designations of older legions. Therefore, Augustus had three legions called »legio III« at his disposal, and legions IV, V and VI each existed twice. To be able to distinguish these military units, they were given unique epithets from the early first century AD onward. These epithets could either refer to the legionnaires’ place of origin or to regions in which they had served successfully for a significant amount of time. Additionally, military virtues of a legion would become a part of its name. Popular examples are »victrix,« the »victorious one,« or »pia fidelis« for a »dutiful and loyal« legion.
If the name of a legion was attributed, for instance, to Emperor Caesar, this did not mean that the legion had necessarily existed continuously since Caesar’s reign. For example, Emperor Augustus drafted veterans of a former Caesarian legion in order to use them as core members of a newly founded legion. In most cases, the emblem of the Caesarian legions was a bull, based on the zodiac sign »Taurus.« This zodiac sign is attributed to the Goddess Venus, the mythical founder of the Julian imperial house. The symbol of Augustus legions’ was the »capricornus,« Augustus’ zodiac sign.