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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 8,000) 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.
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 tribune s 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 Roman upstarts displayed their skill and prowess, laying the foundation for an eventual political career. Cavalry equipment was purchased 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 decurion s. 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 in the Republican Legion prior to the Marian reforms which abolished the separate classes of troops turning the legion into a professional force, into three separate lines:
- The hastati (sing. hastatus) were the younger ones and formed the front line
- The principes (sing. princeps), men in their prime (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, 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. Under the Marian (named after Gaius Marius) reforms Legions were for the first time organised into Cohorts.
A legion therefore had around 4,800 legionaries 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.
- Legatus Legionis: The overall Legionary commander. This post was generally appointed by the emperor to a man who was a former Tribune and held command for 3 or 4 years, although could serve for a much longer period. In a province with only one legion, the Legatus was also the provincial governor and in provinces with multiple legions, each legion has a Legatus and the provincial governor has overall command of them all.
- Tribunus Laticlavius: Named for the broad striped toga worn by men of senatorial rank, this tribune was appointed by the Emperor or the Senate. Though generally quite young and less experienced than the Tribuni Angusticlavii, he served as second in command of the legion, behind the Legate.
- Praefectus Castrorum: The camp Prefect. Generally he was a long serving veteran who had been promoted through the ranks of the centurions and was 3rd in overall command.
- Tribuni Angusticlavii: Each legion had 5 military tribunes of equestrian (knight) class citizens. They were in many cases career officers and served many of the important administrative tasks of the Legion, but still served in a full tactical command function during engagements.
- Primus Pilus: The "First File" or "First Spear" was the commanding centurion of the first cohort and the senior centurion of the entire Legion. When the Primus Pilus retired he was guaranteed entry into the Equestrian Class. He was paid 60 times the base wage.
- Centurions: Each Legion had 59 or 60 centurions, one to command each century of the 10 cohorts. They were the backbone of the professional army and were the career soldiers who ran the day to day life of the soldiers as well as issuing commands in the field. They were generally moved up from the ranks, but in some cases could be direct appointments from the Emperor or other higher ranking officials. The cohorts were ranked from the First to the Tenth and the Century within each cohort ranked from 1 to 6, with only 5 Century in the First Cohort (For a total of 59 Centurions and the Primus Pilus). The Century that each Centurion commanded was a direct reflection of his rank. (Command of the First Century of the First Cohort was the highest and the 6th Century of the 10th Cohort was the lowest). The 5 Centurions of the First Cohort were called the Primi Ordines (paid 30 times the base wage), and included the Primus Pilus. The Pilus Prior was the commander of the first Century of each Cohort.
- Aquilifer: A single position within the Legion. The Aquilifer was the Legion's Standard or Eagle bearer and was an enormously important and prestigious position. Losing the aquila (eagle) was considered a great dishonor. The next step up would be a post as a Centurion. Paid twice the basic wage.
- Signifer: Each Century had a Signifer (59). He was responsible for the men's pay and savings, and the standard bearer for the Centurial Signum, a spear shaft decorated with medallions and often topped with an open hand to signify the oath of loyalty taken by the soldiers. It was this banner that the men from each individual Century would rally around. A soldier could also gain the position of Discentes signiferorum, or standard bearer in training. Paid twice the basic wage.
- Optio: One for each Centurion (59), they were appointed by the Centurion from within the ranks to act as his second in command. Paid twice the basic wage.
- Tesserarius: (Guard Commander) Again there were 59 of these, or one for each Century. They acted seconds to the Optios. Paid one and a half times the basic wage.
- Cornicen: (Horn blower) They worked hand in hand with the Signifer drawing the attention of the men to the Centurial Signum and issuing the audible commands of the officers.
- Imaginifer: Carried the Standard bearing the image of the Emperor as a constant reminder of the troop's loyalty to him.
References and further reading
- Roman Republic, Roman Empire
- Punic wars
- List of Roman legions