Marian reforms
During the Marian reforms in the 1st century BC, the command structure and make-up of the legions was established in a formal standard. Standard "centuriae" consisted of 80 men each. The first cohort was made up of five double-strength centuries (160 men). The centurion of its first century automatically was senior in the legion known as the "primus pilus". The "primus pilus" could be promoted to "praefectus castrorum" (camp prefect). The "praefectus castrorum" was in charge of the daily administration of a legion.