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Roman legion
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Roman legion

See 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 (later 8000) infantry soldiers and several hundred cavalrymen. Legions were named and numbered; about 50 have been identified, although there were never that many in existence at any one time. Usually there were 28 Legions plus their Auxiliaries, with more raised as needed or as able.

Table of contents
1 History
2 Organization
3 Symbols
4 References and further reading
5 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 became more sophisticated, from the classic phalanx to the manipular system, and allowed important tactical innovations. Later in the Roman Empire, the legion was commonly reinforced by allied troops, the allae.

Throughout the history of Rome's Late Republic and Imperial era, 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. By the 1st Century BC the threat of the Legions under a demagogue was recognized. Governors could not leave their provinces with their Legions. When Julius Caesar crossed the Rubicon he left his provinces and came to Italy under arms. This last precipitated a constitutional crisis.


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 by campaign. The shift to more permanent legions came about primarily for domestic reasons, i.e. to make them loyal to the Emperor, not their generals. In The Empire, the legion was standardized, with symbols and an individual history where men were proud to serve. 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. The cavalry was originally the most prestigious unit, where wealthy young Romans started to be noticed before the starting of their political career. Cavalry equipment was paid by each of the cavalrymen and consisted of a round shield, helmet, body armour, sword and one or more javelins. 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 of 30 men. These men were commanded by decurions. Additional to this heavy cavalry, there would be the light cavalry levied from poor citizens and wealthy young citizens not old enough to be in the hastati or the equites.

Light infantry or velites. The velites were basically javelin throwers who 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 and short spear(pillum). 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 manipless, 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, millstone, a mule and cooking pot (depending on duration of tour).

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 of which there were six to ten, substitutes the manipule as the basic tactical 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.

Auxiliaries, each Legion had a same size or near same size auxiliary which contained specialist units, engineers and pioneers, artillerymen and siege craftsmen, service and support units plus units made up of non-citizens(who were granted Roman citizenship upon discharge) and undesireables. These were usually formed into complete units such as light cavalry, light infantry, and laborers.


From 104 BCE onwards, each legion used an eagle as its standard. The standard was carried by an officer known as an aquilifer, and its loss was considered to be a very serious embarrassment.

References and further reading

See also