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 (later formalised as a
centurion),
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 (from
Latin:
censeō – accounting of the people) 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 (multitude). 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 (in which the clan was annihilated). 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 (two per consul), other units were levied by campaign. Rome's Italian allies were required to provide approximately ten cohorts (auxilia were not organised into legions) to support each Roman Legion. In the middle of the Republic, legions were composed of the following units: •
Equites (cavalry): 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 (plus the
velites that normally enlarged the number to about 4,200), the legion only had around 300 horsemen, divided into ten units (
turmae) 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 (though not always) 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 (
light infantry): 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 (
caligae) were also an effective weapon against a fallen enemy. Heavy infantry was subdivided, according to experience, into three separate lines of troops: • The
hastati (:
hastatus): 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 (:
princeps): 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 (:
triarius): 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 (spears) rather than the
pilum and
gladius (the
hastati and
principes stopped using spears in 387 BC). 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. Each of these three lines was subdivided into (usually ten) chief tactical units called
maniples. A maniple consisted of two
centuries and was commanded by the senior of the two
centurions. At this time, each century of
hastati and
principes consisted of 60 men; a century of
triarii was 30 men. These 3,000 men (twenty maniples of 120 men, and ten maniples of 60 men), together with about 1,200 velites and 300 cavalry gave the mid Republican ("manipular") legion a nominal strength of about 4,500 men.
Late Republic (107–27 BC) Each century had its own standard and was made up of ten units (
contubernia) of eight men who shared a tent, a millstone, a mule and
cooking pot. Full Roman citizenship was open to all the regions of Italy. At the same time, the three different types of heavy infantry were replaced by a single, standard type based on the
principes: armed with two heavy javelins called
pila (singular
pilum), the short sword called
gladius, chain mail (
lorica hamata), helmet and rectangular shield (
scutum). The role of allied legions would eventually be taken up by contingents of allied auxiliary troops, called
auxilia.
Auxilia contained
immunes (specialist units), engineers and pioneers, artillerymen and craftsmen, service and support personnel and irregular units made up of non-citizens, mercenaries and local militia. These were usually formed into complete units such as light cavalry,
light infantry or
velites, and labourers. There was also a
reconnaissance squad of ten or more light
mounted infantry called
speculatores, who could also serve as messengers or even as an early form of
military intelligence service. A typical legion of this period had 5,120 legionaries as well as a large number of camp followers, servants and slaves. Legions could contain as many as 11,000 fighting men when including the auxiliaries. During the Later Roman Empire, the legion was reduced in size to 1,000 to allow for easier provisioning and to expand the regions under surveillance. Numbers would also vary depending on casualties suffered during a campaign;
Julius Caesar's legions during his campaign in Gaul often only had around 3,500 men. Tactics were not very different from the past, but their effectiveness was largely improved because of the professional training of the soldiers. Throughout the history of Rome's Late Republic, the legions played an important political role. By the 1st century BC, the threat of the legions under a
demagogue was recognised.
Roman governors were not allowed to leave their provinces with their legions. When
Julius Caesar broke this rule, leaving his province of Gaul and crossing the Rubicon into Italy, he precipitated a
constitutional crisis. This crisis and the
civil wars which followed brought an end to the Republic and led to the foundation of the
Empire under
Augustus in 27 BC.
Early Empire (27 BC–AD 284) Generals, during the recent Republican civil wars, had formed their own legions and numbered them as they wished. During this time, there was a high incidence of
Gemina (twin) legions, where two legions were consolidated into a single organisation (and was later made official and put under a
legatus and six
duces). At the end of the civil war against
Mark Antony, Augustus was left with around fifty legions, with several double counts (multiple Legio Xs for instance). For political and economic reasons, Augustus reduced the number of legions to 28 (which shrank to 25 after the
Battle of the Teutoburg Forest, in which three legions were completely destroyed). Beside streamlining the army, Augustus also regulated the soldiers' pay. At the same time, he greatly increased the number of auxiliaries to the point where they were equal in number to the legionaries. He also created the
Praetorian Guard along with a permanent
Roman navy where served the
liberti, or freed slaves. The legions also became permanent at this time, and not recruited for particular campaigns. They were also allocated to static bases with permanent
castra legionaria (legionary fortresses). Augustus' military policies proved sound and cost effective, and were generally followed by his successors. These emperors would carefully add new legions, as circumstances required or permitted, until the strength of the standing army stood at around 30 legions (hence the wry remark of the philosopher
Favorinus that
It is ill arguing with the master of 30 legions). With each legion having 5,120 legionaries usually supported by an equal number of auxiliary troops (according to Tacitus), the total force available to a legion commander during the
Pax Romana probably ranged from 11,000 downwards, with the more prestigious legions and those stationed on hostile borders or in restive provinces tending to have more auxiliaries. By the time of the emperor
Severus, 193–211, the auxiliaries may have composed 55 to 60% of the army, 250,000 of 447,000. Some legions may have even been reinforced at times with units making the associated force near 15,000–16,000 or about the size of a modern
division. Throughout the Imperial era, the legions played an important political role. Their actions could secure the empire for a
usurper or take it away. For example, the defeat of
Vitellius in the
Year of the Four Emperors was decided when the
Danubian legions chose to support
Vespasian. In the Empire, the legion was standardised, with symbols and an individual history where men were proud to serve. The legion was commanded by a
legatus or
legate. 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 (originally this tribune commanded the legion). There would also be a group of officers for the medical staff, the engineers, record-keepers, the
praefectus castrorum (commander of the camp) and other specialists such as priests and musicians.
Later Empire (from 284 AD) In the
Later Roman Empire, the number of legions was increased and the
Roman army expanded. There is no evidence to suggest that legions changed in form before the
Tetrarchy, although there is evidence that they were smaller than the paper strengths usually quoted. The final form of the legion originated with the elite
legiones palatinae created by
Diocletian and the Tetrarchs. These were infantry units of around 1,000 men rather than the 5,000, including cavalry, of the old legions. The earliest
legiones palatinae were the
Lanciarii,
Joviani,
Herculiani and
Divitenses. The 4th century saw a very large number of new, small legions created, a process which began under
Constantine II. In addition to the elite
palatini, other legions called
comitatenses and
pseudocomitatenses, along with the
auxilia palatina, provided the infantry of late Roman armies. The
Notitia Dignitatum lists 25
legiones palatinae, 70
legiones comitatenses, 47
legiones pseudocomitatenses and 111
auxilia palatina in the field armies, and a further 47
legiones in the frontier armies. Legion names such as
Honoriani and
Gratianenses found in the
Notitia suggest that the process of creating new legions continued through the 4th century rather than being a single event. The names also suggest that many new legions were formed from
vexillationes or from old legions. In addition, there were 24 vexillationes palatini, 73
vexillationes comitatenses; 305 other units in the Eastern
limitanei and 181 in the Western
limitanei. A rare instance of apparent direct continuity between the legions of the early Empire and those of the post-6th century army was
Legion V Macedonica; created in 43 BC, recorded in the
Notitia Dignitatum as a
legione comitatense under the title of
Quinta Macedonica and surviving in Egypt until the Arab conquest of 637 AD. According to the late Roman writer
Vegetius'
De re militari, each century had a
ballista and each cohort had an
onager, giving the legion a formidable siege train of 59 ballistae and 10 onagers, each manned by 10
libritors (artillerymen) and mounted on wagons drawn by oxen or mules. In addition to attacking cities and fortifications, these would be used to help defend Roman forts and fortified camps (
castra) as well. They would even be employed on occasion, especially in the later Empire, as
field artillery during battles or in support of river crossings. Despite a number of organisational changes, the legion system survived the
fall of the Western Roman Empire. It was continued within the
Eastern Roman Empire until the 7th century, when reforms begun by Emperor
Heraclius to supply the increasing need for soldiers resulted in the
Theme system. Despite this, the Eastern Roman armies continued to be influenced by the earlier Roman legions, and were maintained with similar levels of discipline, strategic prowess, and organization. ==Legionary ranks==