A division of the army in ancient Rome. Legions evolved from the citizen militia that equipped itself in times of crisis for defence of the state. During the Second Punic War Scipio Africanus reorganized the battle array and improved the army’s tactics. Under Marius, men of no property began to be recruited, a professional army appeared and new training methods were introduced. Ten cohorts, 6000 soldiers, with standards formed a named and numbered legion with an eagle standard. The cohorts, divided into six centuries (100 men in each century) commanded by a centurion, became the main tactical unit of the army. Cavalry and auxiliaries supported each regiment.

Augustus established a standing army to man the frontiers of the empire. There appears to have been 28 permanent legions, each having a number and an honorific title. Severus added three legions; Constantine increased the number but limited them to 1000 men each to allow flexibility and to avoid mutiny. He also placed them under equestrian prefects instead of the traditional senatorial legates and placed a Christian symbol on their standards. On retirement a veteran in the early days earned a land grant in a “colony” where he continued to act as a Romanizing and pacifying influence throughout the empire, but from the time of Augustus it was more useful for him to receive money rather than land. Many nevertheless settled in the area where they had served, thus effectively “colonizing” it.