Roman Military Organization
Contributed by David Verne
The Roman military was highly organized, especially in comparison to the barbarians surrounding the Empire. The smallest unit was the contubernium, which translates into shared tent, and was made up of eight men who shared a tent. There were also two servants or slaves assigned to the contubernium to take care of the unit's pack mule, cook, repair equipment, etc., but they aren't counted since they were noncombatants. The unit was commanded by a Decanus, a junior NCO who was elected by the contubernium from within the unit.
The next unit up was a century, which included 10 contubernia for a total of 80 soldiers and the additional 20 servants. This was the basic tactical unit and each century had their own standard. They were commanded by a centurion, who was comparable to a junior officer in modern rank structure, but they were still considered enlisted. They were promoted from the ranks by their commanders or the Senate. The century's second in command was the optio, and they were in charge of training. During battle, centurions led from the front rank while the optio was in the opposite corner of the back rank to make sure no soldiers ran away.
Cohorts were made up of six centuries, 480 men, and in battle, generals would normally move cohorts around as a unit, not splitting up the centuries. There was no special rank for the commander of a cohort; the most experienced centurion of the six in the cohort would issue orders to the cohort as well as his century.
Legions had 10 cohorts for a total of 5,248 men. The first cohort was different then the other nine cohorts and was made up of five double strength centuries totaling 800 men. Most of these extra men were experts like blacksmiths, carpenters, and engineers. These five centuries were commanded by the five most experienced centurions in the legion, with the most experienced of these five having the title of primus pilus and was the highest ranking enlisted in the legion.
The three officers in command of the legion were the camp prefect, the military tribune, and the legate. The camp prefect was a former primus pilus and was in charge of supply and fortifications. It was a cushy but important job, perfect for an older soldier with decades of experience. They were appointed by the commander of the legion, but once appointed, they held the position until retirement. The military tribune acted as a staff officer for the legate and was normally a Senator's son starting his political career. The legate was appointed by the Emperor or the Senate and was the highest ranking officer in the legion. There was also a 128 man cavalry unit that supported the legion.