What was the structure of a legion?

The number of troops in a legion varied from 3,000 to 5,000 throughout the Roman Empire but generally consisted of 10 cohorts (each with 500 men) with the first cohort double strength and featuring the best soldiers in the legion. Every 80 men (century) was led by a centurion, every cohort was made up of centuries which were led by another centurion and so on.

To carry out tasks removed from war, the legion would be split into groups of one thousand men known as Vexallations. These groups would carry out works such as fort building or food gathering.