A centurion was a professional officer of the Roman army. Centurions commanded a century of soldiers and noncombatants. As a centurion grew in seniority, he could command a cohort, and eventually become primus pilus, Latin for "first spear", of a Roman legion. The centurions of a cohort were pilus prior, pilus posterior, princeps prior, princeps posterior, hastatus prior, and hastatus posterior for cohorts II-X.

The centurion's uniform was marked by two alterations from standard Roman uniform: his helmet crest was side to side instead of back to front, and he wore greaves. The centurion also carried a vine staff as a badge of office, sometimes used to beat delinquent soldiers.

The Greek term for centurion was hekatontarchos.