Roman Legions: From Tribal Levy to Imperial Legion

Considerable changes the tactical formation of the Roman Army had taken place since the Punic Wars. Some were introduced by Marius, or by Caesar a consequence of his campaigns. The Roman soldier as to arms, equipment and minor tactics, was to all intents and purposes the same as be bad been in the time of Hannibal. Our knowledge of the Roman army comes from three authors who provide us with some evidence of the structure and behaviour of the early Roman army: Livy, Polybius and, of course, Caesar himself. Rome’s success as a military power seems to have been due more to its ability to learn from its mistakes and evolve over time.

History of the Roman Army: Tribal Levy

Until c. 550 BC, there was probably no “national” Roman army, but a series of clan-based war-bands, which only coalesced into a united force in periods of serious external threat. These war-bands consisted of around 3,000 men and were organized on the basis of tribal groups, called a legio or a ‘levying’. Each tribe contributed 100 men towards the total force – the origin of the ‘century’ of Caesar’s legion. The wealthy elites in the tribe were relied upon to supply the cavalry for the army, as only they could afford expensive equipment and horses.

History of the Roman Army: The Roman Phalanx

In the early days of the Roman Republic, the Roman army became far more formalized, along the hierarchical lines society was taking and military tactics were influenced by the methods used by the Greeks by 675 BC and reached the Italy-based Etruscans by the early 7th century BC.

The army was organized as a conscript levy of all male citizens. Membership in the army was marked by stringent property- and census-requirements for even the common soldier.

The original Roman army was made up of hoplites, whose main strategy was forming into a phalanx. This involved the soldiers standing densely packed ranks of heavily armed spearmen. Just before contact with the enemy, the soldiers moved in very close together so that each man’s shield helped to protect the man on his left.

With only about three feet between the rows of soldiers, the Romans would move towards the enemy. The phalanx was a very difficult barrier to break through. If a man in the front was killed, he was replaced by the man behind. The shields would not only be used to protect the soldiers, but to push the enemy soldiers to the ground or to make them break ranks.

The phalanx formation was used for hundreds of years. However it proved inadequate against lightly-armed, fast-moving cavalry, and may have been difficult to adopt in broken or hill terrain.

According to Livy, there were six such classes – all based on their possession of wealth (that was defined by asses or small copper coins). The first three classes fought as the traditional hoplites, armed with spears and shields – although the armaments decreased based on their economic statuses. The fourth class was only armed with spears and javelins, while the fifth class was scantily armed with slings. Finally, the sixth (and poorest) class was totally exempt from military service. This system once again alludes to how the early Roman army was formed on truly nationalistic values. Simply put, these men left their homes and went to war to protect (or increase) their own lands and wealth, as opposed to opting for just a military ‘career’.

History of the Roman Army: The Roman Maniple

By the early third century BC, during the Samnite Wars (343–290 BC), the Roman Army would switch to began to adopt less dense formations. The Roman phalanx was reorganized into a series of small tactical units called manipuli (maniples). The very term manipulus means ‘a handful’, and thus its early standard incorporated a pole with a handful of hay placed around it.

Typically, each of Rome’s two consuls would have two Legions at his disposal. A Legion was commanded by six tribunals; a pair of tribunals would command the Legion for two months at a time, switching off command with each other every day and rotating to the next pair at the end of two months.

Roman Manipular Legion

The early Roman Manipular Legion, used from the fourth century B.C. until the Marian Reforms of 107 B.C., was the largest and most basic unit of the army’s composition. The Roman Army consisted of four Legions, each with the strength of roughly 4200 infantrymen.

The Legion, when formed up for battle, had three lines of infantry: first were the hastati, then the principes, and finally the veteran triarii. Each of these three lines contained five manipuli of 120 hastati, 120 principes, and sixty triarii. A maniple was further subdivided into two centuriae of sixty each hastati and principes, and thirty triarii. Each century had six squads; a squad, aptly named contubernium (“tenting-together”) in Latin, shared a tent when the Legion went on campaigns.

Manipular Legions were supported by ten thirty-man squadrons (turmae) of equites, light cavalry, and the more loosely organized velites, skirmishing troops.

Tactics of the Roman Manipular Legion – Triplex Acies

In a battle formation they were arranged in three lines (triplex acies) in a chessboard pattern (quincunx). The tactical units were organised into four groups: velites, hastati, principes and triarii.

Tactics of the Roman Manipular Legion – Triplex Acies

The velites were young and inexperienced soldiers. They were at the front and their main task was to make the early attacks on the enemy. When they were recalled, the velites passed through the open ranks and went to the back.

The front rank was now made up of the hastati. When they were about 35 metres from the enemy they threw their javelins (pill). Drawing their swords, they now charged the enemy. Behind them, the rest of the Roman Army threw their javelins over the heads of the advancing hastati. If the charge proved unsuccessful, the hastati withdrew and re-formed behind the rest of the army.

It was now the turn of the principes to attack. The principes were the best soldiers that the Roman army had available. The enemy, exhausted by the previous attacks, now had to face fresh and experienced soldiers and, it was usually at this point that they broke formation and ran away. However, if the principes were unsuccessful, the last group, the triarii, would be brought forward.

The cavalry would be placed on the wings, to oppose the enemy cavalry, prevent outflanking manoeuvres and carry out pursuit of the enemy.

The original smaller tactical unit of the Romans had been the century. It next became the maniple of two centuries. Later the three maniples of the hastati, principes and triarii, with some cavalry and velites, were merged into one body called a cohort.

The Auxiliaries (Socii)

The origin of auxiliary troops lies in Republican times, when Rome, following Greek tradition, started to call for a growing number of mercenaries. Towards the end of the Republic, in campaigns outside Italy, Roman legions were frequently supported by levies of local troops also from among Rome’s allies (socii) or from defeated kingdoms. Marius’ reform, which disbanded the legionary cavalry, led Rome to use only auxiliaries as mounted troops; from the non, they continued to develop.

History of the Roman Army: The Roman Cohorts

Later, in 107 BCE, Marius would institute the Marian reforms, creating the “Roman legions” of popular imagination. Marius proposed radical alterations with the intention of creating a more professional, permanent, and dynamic Roman army. The reforms introducing the standardized legionary, the cohort unit and drastically altering the property and weaponry requirements for recruitment. The reforms also put the responsibility of supplying and managing an army in the hands of the general. Marius also granted citizenship and land to all Roman soldiers.

Marius is thought to have been responsible for the change from maniples to cohorts but it is likely that both systems could have been in place together for a period. The cohort system did away with the different types of soldier, replacing them with a flexible body of similarly armed men.

The Structure of the Imperial Legion

The most basic unit of the Roman army was the contubernium, the tentmates. It was thought to have contained , composed of 8 men who shared a tent, a mule, and eating equipment. Soldiers of such a unit were called contubernales.

Ten contubernia constituted a century. Two centuries made up a maniple, and 3 maniples made up a cohort, one from each of the lines of the older manipular legions. A legion had ten cohorts. So each century contained 80 soldiers, each cohort was 480 men strong and the legion 4,800 infantry soldiers at optimum strength.

Each maniple had two centurions, a senior and a junior, and to each centurion there was a sub-centurion or optio. These, like our company officers, all served on foot. The senior centurion of the cohort was its commander. While, like the non-commissioned officers of modern armies, the centurions could not rise in rank beyond their own grade, and while their duties were assimilated to these, they more nearly approached, in the extent of their command, our company officers than our sergeants.

The three maniples of the cohort kept their original names from the Consular Legion in the titles of the centurions. Youngest and least experienced units were termed hastati, next principes, and the oldest and most experienced triarii (pilus was a rare alternative name for triarius, the singular of triarii). The Second to Tenth Cohorts each had six centurions, with their full titles from junior to senior, being the hastatus posterior, hastatus prior, princeps posterior, princeps prior, pilus posterior, and pilus prior.

The first legion cohort was usually composed of the best soldiers and constituted an elite in the legion. In general, the prestige of the cohort increased the closer it was to the “first” cohort. The first cohort was made up of five double-strength centuries (160 men each). The centurion of its first century automatically was senior in the legion known as the primus pilus. The primus pilus could be promoted to praefectus castrorum (camp prefect). The praefectus castrorum was in charge of the daily administration of a legion.

The cohort was practically the tactical unit of the legion, and all manoeuvres were by cohorts.

Senatorial Positions in a Legion

Members of Rome’s ruling society were expected to be soldiers first. All tribunes and legion commanders came from the noble classes. The surest way for a senator to gain a governorship or the Consul’s chair was to have proven himself on the battlefield. Military Tribunes (tribuni militum) were elected young officials with aspirations to climb the Cursus Honorum. The Legate and the Tribunus Laticlavius would have been from the senatorial class.