Main Page | See live article | Alphabetical index

Roman legion

Legion redirects here. There is also Legion software and Legion forummer.

The Roman legion (from the Latin legio, meaning levy) was the basic military unit of ancient Rome. It consisted of about 5,000 to 6,000 infantry soldiers and cavalrymen. Legions were named and numbered; about 50 have been identified, although there were never that many in existence at any one time.

Table of contents
1 History
2 Organization
3 References and further reading
4 See also


Originally, in the time of the kings, the legio was the whole Roman army, comprised of levied citizens. At some point, possibly in the beginning of the Roman Republic, the legio was subdivided into two separate legions, each one ascribed to one of the two consuls. In the first years of the Republic, when the warfare was mostly concentrated in raids, it is uncertain if the full manpower of the legions was summoned at one time. Legions become organized in a more formal way in the 4th century BC, as Roman warfare evolved to more frequent and planned operations, and the consular army was raised to two legions. The military tribunes appeared after 331 BC. The internal organization of the legion become more sophisticated, from the classic phalanx to the manipular system, and allowed important tactical innovations.

In the second century BC, consul Gaius Marius instituted sweeping changes which were essentially complete by 60 CE.

Later in the Roman Empire, the legion was commonly reinforced by allied troops, the allae.

In several occasion of the history of Rome, the legions played an important political role. Their actions could secure the empire for an Imperial hopeful or take it away. An example is the defeat of Vitellius in the Year of the four emperors, decided in the moment that the Danubian legions chose to support Vespasian. For much of Roman history the potential power of the legions was acknowledged in that they were legally excluded from Italy proper, they could not cross the Rubicon.

In the Republic, legions had an ephemeral existence. Except for Legio I to IV, which were the consular army (two per consul), other units were levied and disbanded according to necessity. The need for more permanent legions only came when serious threats to the provinces started to appear (Jugurtha in Numidia or the barbaric invasions of the beginning of the 1st century BC). In The Empire, the legion was a perfectly defined entity, with symbols and an individual history (see List of Roman legions and therein for details), where men were proud to serve. Numerous examples of legionary tombstones were the number and name of the legion he served on appear with the soldier's and family names, attest this.


The legion was 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 elected military 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.

In the middle of the Republic, legions were composed of the following units:

Cavalry or equites. Originally the most prestigious unit, where wealthy young Romans started to be noticed before the starting of their political career (cursus honorum). Cavalry equipment was paid by each of the cavalrymen and consisted of a round shield, helmet, body armour, sword and one or more javelins. Contrary to what is depicted in numerous historical movies, Roman cavalry did not make use of stirrups. The cavalry was outnumbered in the legion. In a total of circa 3000 men, the legion had only around 300 horsemen, divided into 10 units (turmae) of 30 men. The turmae were commanded by decurions. Additional to this heavy cavalry, there would be the light cavalry or velites, levied from poor citizens and wealthy young citizens not old enough to be in the hastati or the equites. The velites did not have a precise formal organization or function in battle, being used where there was need for them.

Heavy Infantry. This was the principal unit of the legion. The heavy infantry was composed of citizen legionaries that could afford the equipment composed of bronze helmet, shield, armour (lorica segmentata) and javelin (the pilum). The preferred weapon was the gladius, a short sword. The heavy infantry was subdivided, according to the legionaries' experience, into three separate lines:

The hastati (sing. hastatus) were the younger ones and formed the front line
The principes (sing. princeps), men in their late twenties early thirties, composed the second line of the legion
The triarii (sing. triarius) were the veteran soldiers that occupied the rear; only in extreme situations would they be used in battle.

Each of these three lines was subdivided into maniples, the lowest subunit of the army, each consisting of two centuries 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, especially in the less numerous triarii manipules. Each century had its standard and was made up of ten units called contubernia. In a contubernium there would be eight soldiers who shared a tent and cooking pot.

In battle, the manipules were commonly arranged in a chequered formation called quincunx. Principes'\' manipules would cover the open space left by the hastati, and be covered in return by triarii'' manipules.

In the late republic, the cohort substitutes the manipule as the basic tactic unit. The cohort is composed of six to eight centuries and is led by a centurion assisted by an optio, a soldier who could read and write. The senior centurion of the legion was called the primus pilus, a career soldier and advisor to the legate.

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.

References and further reading

See also