This is a summary of the Roman Army rank hierarchy, which made the Roman Legion function as an effective war machine. The following ranks represent the hierarchical structure enforced after the Marian reforms of 107 BC.

Consul. Being elected by the Senate, he was the commander in chief of an army. There were two. Famous consuls: Julius Caesar and Gaius Marius.

Tribune. He was a legion (6,000 men) commanding officer. He was elected by the Tribal Assembly (Roman House of Representative).

–  Lagate (Legatus). A legion commander acting as such in a foreign region, and he could temporarily replace a Tribune.

Praefectus Castrorum. Having an equestrian rank (cavalry), he was the third in the chain of command as he could replace either a Tribune or a Legate.

Centurion. He was the toughest and fiercest soldier of a legion. This rank was divided into Ordinatus (commander of a century of the second cohort), Primus Ordinus (commander of a first cohort century), and Primus Pilus (the senior centurion, who was commander of the first, rightmost cohort century). The Primus Pilus centurion was also commander of a cohort (600-man unit). According to the number of men he commanded, his rank was the equivalent of today’s captain. However, he was already at the top of his military career as he could not be raised to a higher rank; thus, from this point of view, a centurion was the equivalent of today’s Sergeant Major. In the battlefield, he could be spotted by the crosswise or transverse crest on top of his helmet.

Optio. Commander of a 30-man unit and second in command in a century. He wore a lengthwise or sagittalwise crest on top of his helmet.

Decanus. Commander of a contubernium (an 8-man squad unit).

Miles. Ordinary soldier, who received basic pay.

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