page_title: Imperial Roman army
section_title: Legions
hierarchical_section_title: Imperial Roman army / Ranks, role and pay / Senior officers (tribuni militum, praefecti and legati) / Legions
caption_attribution_description: English: Sacrifice scene during a census: Midde part of a plaque from the Altar of Domitius Ahenobarbus known as the “Census frieze”. Marble, Roman artwork of the late 2nd century BC. From the Campo Marzio, Rome. Français&#160;: Scène de sacrifice pendant un recensement&#160;: partie centrale d'une plaque de l'autel de Domitius Ahenobarbus, connue sous le nom de la «&#160;frise du recensement&#160;». Marbre, œuvre romaine de la fin du IIe siècle av. J.-C. Provenance&#160;: Champ de Mars, Rome.
context_page_description: The Imperial Roman army was the terrestrial armed forces deployed by the Roman Empire from about 30 BC to 476 AD, the final period in the long history of the Roman army. This period is sometimes split into the Principate and Dominate periods.
  Under Augustus, the army consisted of legions, eventually auxilia and also numeri.
  Legions were formations numbering about 5,000 heavy infantry recruited from the ranks of Roman citizens only, transformed from earlier mixed conscript and volunteer soldiers serving an average of 10 years, to all-volunteer units of long-term professionals serving a standard 25-year term.
  Auxilia were organised into regiments of about 500 strong under Augustus, a tenth the size of legions, recruited from the peregrini or non-citizen inhabitants of the empire who constituted approximately 90 percent of the Empire's population in the 1st century AD. The auxilia provided virtually all the army's cavalry, light infantry, archers and other specialists, in addition to heavy infantry equipped in a similar manner to legionaries.
  Numeri were allied native units from outside the Empire who fought alongside the regular forces on a mercenary basis.
caption: A Roman military tribune (centre) of the late Republic. Note the horse-hair plume on the helmet, bronze muscle cuirass, mantle, sash indicating knightly rank, pteruges. Detail from bas-relief on the Altar of Cn. Domitius Ahenobarbus, about 122 BC. Musée du Louvre, Paris
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