Roman legion - Wikipedia

The Roman legion was the primary large military unit of ancient Rome. It consisted of about 5,000 to 6,000 infantry soldiers. Legions were named and numbered; about 50 have been identified, although there were never that many in existence at any one time.

The origins of the legion are uncertain; references to legions existing in the time of the kings are probably later interpretations not based on facts. The first believable account is in Polybius, and reflects organization around 200 BC. By that time the legion was composed of several different lines of soldiers, based on the weight and strength of their armor and weapons, and grouped into 30 maniples[?], each consisting of two centuries, the maniple being commanded by the senior of the two centurions. Centuries were nominally 100 soldiers each (thus the name), but in practice might be as few as 60.

The consul Gaius Marius instituted sweeping changes which were essentially complete by 60 CE.

The legion would be commanded by a legate or "legatus[?]". Aged around thirty he would usually be a senator on a three year appointment. Immediately subordinate to the legate would be six tribunes - five would be staff officers and the remaining one would be a noble heading for the Senate. There would also be a group of officers for the medical staff, the engineers, record-keepers and the praefecti castrorum[?] (commander of the camp) as well as other specialists such as priests and musicians.

A legion would consist of ten cohorts[?], with six centuries in each (the first cohort could contain eight centuries, but this was not usual in 60 CE). Each cohort was commanded by a centurion. The senior centurion was called the prime pilus[?] - he would be a career soldier and an advisor to the legate. Each century would also be commanded by a centurion, to assist each century centurion would be an optio[?], a soldier who could read and write.

Each century was made up of ten units called contubernia. In a contubernium there would be eight soldiers who shared a tent and cooking pot.

As well as the foot soldiers there would a cavalry unit called an alae. Usually recruited from non-Roman allies they would still have a Roman commander, a decurion[?]. Indicative of the low regard the Romans had for cavalry, this unit would often number no more than 300 men.

A legion therefore had around 4,800 men-at-arms as well as a large number of camp followers, servants and slaves. Legions could contain as many as 6,000 fighting men although at times in Roman history the number was reduced to 1,000 to curb the power of mutinous commanders. Julius Caesar's legions had only around 3,500 men.

The Legionary

Called miles ("soldier") or legionarius ("legionary") in Latin, the Roman soldier was (usually) a Roman citizen[?] under 45 years of age. The soldier enlisted for twenty years of service, a change from early practice of enlisting only for the duration of a campaign.

On the march in unfriendly terrain the Legionary would be loaded down with between three and fourteen days worth of food, armour (lorica segmentata) and shield (scutum), helmet, two javelins (one heavy pilum and one light), short sword (gladius), dagger (pugio), a waterskin and some tools.

The Roman soldier was trained especially hard, discipline was the base of the army's success and the soldiers were relentlessly and constantly trained both with weapons but especially with drill - forced marches with full load and in tight formation were frequent. And infractions were heavily punished by the centurions.