15. The Roman Army Underwent Many Changes
The Roman army’s largest military unit was the legion, and it changed a lot in its centuries-long existence. In the mid-Roman Republic, it numbered about 3,000 heavy infantry divided into maniples of 120 soldiers, each comprised of two 60-man centuries. There were also 1,200 skirmishers and 300 cavalry, for a total of around 4,500 legionaries. In the late Republic, the centuries grew to 80 men, and six centuries were grouped into a cohort of 480 legionaries. A legion contained nine such standard cohorts, plus a first cohort of the best soldiers, made of five double-strength centuries of 160 men each. That meant a total nominal legion strength of 5,120 men, but in practice, about 4,500 was the norm. In the early Roman Empire, Augustus had 30 legions, stationed along the borders.
They were supported by auxiliary troops of non-citizens, who were granted Roman citizenship at the end of their service. Each legion was led by a Legate, usually a senator appointed by the emperor. Below him were six tribunes, one from the senatorial class who served as the legion’s second in command, and five from the lower equestrian class. Third in command was the Camp Prefect, usually a veteran ranker from the lower classes. He had typically served 25 years, including a stint as a centurion of the first cohort. Next came the centurions, officers promoted from the ranks to command the legion’s centuries and cohorts. Beneath them came optios, equivalent to First Sergeants, one for each century, assisted by guard commanders, one per optio, and the common legionaries.
