Roman legion
The Roman legion was the largest military unit of the Roman army, composed of Roman citizens serving as legionaries. During the Roman Republic the manipular legion comprised 4,200 infantry and 300 cavalry. In late Republican times the legions were formed of 5,200 men and were restructured around 10 cohorts, the first cohort being double strength. This structure persisted throughout the Principate and middle Empire, before further changes in the fourth century resulted in new formations of around 1,000 men.
Size
The size of a typical legion varied throughout the history of ancient Rome, with complements ranging from 4,200 legionaries and 300 equites in the Republic, to 5,500 in the Imperial period, when most legions were led by a Roman Imperial Legate.A legion had 4,800 legionaries from the late republic to the time of Julius Caesar. It expanded to 5,280 men plus 120 auxiliaries in the Imperial period. These are typical field strengths while "paper strength" was slightly higher.
In the early Roman Kingdom the term legion may have meant the entire Roman army, but sources on this period are few and unreliable. The subsequent organisation of legions varied greatly over time but legions were typically composed of around five thousand soldiers. During much of the republican era, a legion was divided into three lines, each of ten maniples. In the late Republic and much of the imperial period, a legion was divided into ten cohorts, each of six centuries. Legions also included a small ala, or cavalry unit. By the third century AD, the legion was a much smaller unit of about 1,000 to 1,500 men, and there were more of them. In the fourth century AD, East Roman border guard legions may have become even smaller. In terms of organization and function, the republican era legion may have been influenced by the ancient Greek and Macedonian phalanx.
Function and constitution
For most of the Roman Imperial period, the legions formed the Roman army's elite heavy infantry, recruited exclusively from Roman citizens, while the remainder of the army consisted of auxiliaries, who provided additional infantry and the vast majority of the Roman cavalry. The Roman army, for most of the Imperial period, consisted mostly of auxiliaries rather than legions.Longevity
Many of the legions founded before 40 BC were still active until at least the fifth century, notably Legio V Macedonica, which was founded by Augustus in 43 BC and was in Egypt in the seventh century during the Islamic conquest of Egypt.On the other hand, Legio XVII, Legio XVIII and Legio XIX, founded by Augustus around 41 BC, were destroyed by a Germanic alliance led by Arminius in the Varian Disaster and never raised again by the Romans thereafter.
Evolution
Almost nothing is known about the legion of the Roman Kingdom period that could have included 1000 men from each of the three original Roman tribes. The earliest surviving detailed description comes from Polybius, who was writing and his account most likely was influenced by the organization of the Roman army after the defeat of Hannibal in the Punic wars some 50 years earlier.The legions of the Republic were only conscripted in times of conflict and usually limited to four legions, two to be commanded by each consul, though more could be levied if needed. Legionaries lacked the opportunity of a military career; they were not paid well, their primary form of income being what they could loot from the battlefield, and were simply called upon when needed and returned to their civilian lives when they were no longer required.
In terms of organization and function, the early Republican era military was inherited from the Etruscans and seemingly influenced by the ancient Greek and Macedonian phalanx.
After a crushing defeat at the Battle of the Allia, in 387 BC the military structure was reformed. Under the Camillan system the legions were initially structured based on social class, with the poorest being the first line of the formation. The legionaries most often fought with hastae and scuta in a checkered maniple formation with assistance from skirmishers. The exception to this was the triarii, the final line of the formation who instead fought as hoplites, using Greek clipei and whose wealth could afford them gladii in the case of a broken spear.
By the 3rd century BC, this system was seen to be inefficient. Under the new Polybian system the ranks were no longer structured by wealth, and instead by age and experience. All legionaries had their hastae replaced by gladii, along with two pila, which were used as an opening volley before melee. The former classes of poor legionaries, the accensi, rorarii, and leves were replaced by the velites. Unit sizes were also expanded.
Non-citizens or peregrini were also offered a position in the military as auxiliaries.
The Republican legion evolved from 3,000 men in the Roman Republic to over 5,200 men in the Roman Empire, consisting of centuries as the basic units. Until the middle of the first century AD, ten cohorts made up a Roman legion. This was later changed to nine cohorts of standard size with the first cohort being of double strength.
By the fourth century AD, the legion was a much smaller unit of about 1,000 to 1,500 men, and there were more of them. This had come about as the large formation legion and auxiliary unit, 10,000 men, was broken down into smaller units – originally temporary detachments – to cover more territory.
In the fourth century AD, East Roman border guard legions may have become even smaller.
History
Roman Kingdom ( to 509 BC)
In the period before the raising of the legio and the early years of the Roman Kingdom and the Roman Republic, forces are described as being organised into centuriae of roughly one hundred men. These centuries were grouped together as required and answered to the leader who had hired or raised them. Such independent organisation persisted until the 2nd century BC amongst light infantry and cavalry, but was discarded completely in later periods with the supporting role taken instead by allied troops. The roles of century leader, second in command and standard bearer are referenced in this early period.Rome's early period is undocumented and shrouded in myths, but those myths tell that during the rule of Servius Tullius, the census was introduced. With this all Roman able-bodied, property-owning male citizens were divided into five classes for military service based on their wealth and then organised into centuries as sub-units of the greater Roman army or legio. Joining the army was both a duty and a distinguishing mark of Roman citizenship; the wealthiest land owners performed the most years of military service. These individuals would have had the most to lose should the state have fallen.
Mid Republic (509–107 BC)
At some point after the overthrow of the Roman monarchy 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 warfare was mostly concentrated on raiding, it is uncertain if the full manpower of the legions was summoned at any one time. In 494 BC, when three foreign threats emerged, the dictator Manius Valerius Maximus raised ten legions which Livy says was a greater number than had been raised previously at any one time.Also, some warfare was still conducted by Roman forces outside the legionary structure, the most famous example being the campaign in 479 BC by the clan army of gens Fabia against the Etruscan city of Veii. Legions became more formally organised in the 4th century BC, as Roman warfare evolved to more frequent and planned operations, and the consular army was raised to two legions each.
In the Republic, legions had an ephemeral existence. Except for Legio I to IV, which were the consular armies, other units were levied by campaign. Rome's Italian allies were required to provide approximately ten cohorts to support each Roman Legion.
In the middle of the Republic, legions were composed of the following units:
- Equites : the cavalry was originally the most prestigious unit, where wealthy young Roman men 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 lances. The cavalry was outnumbered in the legion. In a total of men, the legion only had around 300 horsemen, divided into ten units of 30 men. These men were commanded by decurions. In addition to 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. In battle, they were used to disrupt and outflank enemy infantry formations and to fight off enemy cavalry. In the latter type of engagement, they would often dismount some or all of the horsemen to fight a stationary battle on foot, an unusual tactic for the time, but one that offered significant advantages in stability and agility in a time before stirrups.
- Velites : these were mainly poorer citizens who could not afford to equip themselves properly. Their primary function was to act as skirmishers – javelin-throwers, who would engage the enemy early in order either to harass them or to cover the movement of troops behind them. After throwing their javelins, they would retreat through the gaps between the maniples, screened from the attack of the enemy by the heavy infantry lines. With the shortage of cavalry in the army of the early to mid Republican army, the velites were also used as scouts. They did not have a precise formal organisation or formation.
- 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 a bronze helmet, shield, sword, armour and pilum, a heavy javelin whose range was about 30 metres. After the Second Punic War, the preferred weapon for the hastati and principes was the gladius, a short sword. Their hobnailed sandals were also an effective weapon against a fallen enemy. Heavy infantry was subdivided, according to experience, into three separate lines of troops:
- * The hastati : these consisted of raw or inexperienced soldiers, considered to be less reliable than legionaries of several years' service. The Hastati were placed at the front for several reasons. One reason is the city of Rome could ill-afford to lose experienced soldiers, so they put the greenest soldiers at the front. If they survived, the hastati would gain invaluable experience. Another reason is if the newest soldiers succumbed to battle nerves and broke and tried to run, then there were experienced soldiers behind them to stiffen their resolve.
- * The principes : these were the more experienced soldiers, often better equipped than the hastati, and having more experience on the battlefield, they would take up the second line in the battle in the event the Hastati failed or fled. They were the second wave in an early Republican Legion.
- * The triarii : these were the veteran soldiers, to be used in battle only in extreme situations; they rested one knee down when not engaged in combat. The triarii served primarily as reserves or barrier troops designed to backstop the hastati and principes, and were equipped with long hastae rather than the pilum and gladius. Thus armed, they fought in a phalanx formation. The sight of an advancing armored formation of triarii legionaries frequently discouraged exultant enemies in pursuit of retreating hastati and principes troops. Ad triarios redisse – To fall back upon the triarii – was a Roman idiom meaning to use one's last resort.