
- Imperial Roman legionaries in tight formation, a relief from Glanum, a Roman town in what is now southern France that was inhabited from 27 BC to 260 AD (when it was sacked by invading Alemanni).
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- ROMAN LEGION (Wiki, Excerpts): The Roman legion was the largest military unit of the Roman army, composed of 4,200 infantry and 300 equites (cavalry) in the period of the Roman Republic (509 BC27 BC); and was composed of 5,200 infantry and 120 auxilia in the period of the Roman Empire (27 BC AD 1453)..
- Roman Republic. 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 circa 3,000 men, (plus the velites that normally enlarged the number to about 4,200), the legion only had around 300 horsemen, divided into 10 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): The velites 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 organization 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 an iron helmet, shield, armour and pilum, a heavy javelin whose range was about 30 meters.
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. Prior to the Marian reforms (see below), the heavy infantry was subdivided, according to experience, into 3 separate lines of troops:
- The hastati (sing. hastatus) 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/tus 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 (sing. 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 before the military reforms of Marius.
- The triarii (sing. triarius) 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...More,
https://en.wikipedia.org/wiki/Roman_legion