Marian reforms
The "centuria" was the pivotal tactical unit of a Roman legion after the Marian reforms of 107 BC. It originally consisted of a hundred soldiers; later 80 distributed among 10 "contubernia", with support staff making up the remainder of the 100 men. Each "contubernium" (the minimal unit in the Roman legion) consisted of 8 soldiers who lived in the same tent while on campaign or the same bunk room in barracks. "Centuriae" were grouped by pairs forming maniples, and later into 6 century cohorts.