Roman legions were the backbone of the Roman army. Initially conscripted but later made up of professional soldiers, many from foreign lands. The legions played a significant role in spreading foreign customs across the empire.
In the early days of Rome, Roman legions were conscripted out of the population whenever required. The Roman word “legio” meant conscription in reference to a given year’s mobilized forces.
The early Roman army wasn’t professional but made up of the various census classes of citizen who at the end of the war season would return to their fields and daily lives. Thus there was effectively a new army every year, with relatively low levels of training, few bonds between individuals, and no particular attachment to their unit.
The number of citizens called to arms grew in line with population increase and as the wars and economic wealth also increased: The Roman legion no longer represented the entirety of the year’s conscription but the largest unit of military force into which citizens would be assigned on the day of conscription.
General Marius at the time of the Republic made fundamental changes to conscript a professional standing army. This had numerous advantages such as highly trained units, which were quickly able to engage in action. However it also had unexpected effects on the Roman Republic as the fealty of soldiers became more closely aligned to the individual generals who might themselves engage politically and in civil wars.
Structure of the Roman Legion
Six elected Tribunes, in pairs, took two monthly turns to command the legion. A Roman legion included about 4200 legionaries and 300 equites (cavalry). On the battle field they were set out in three rows (“triplex acies”) of well armed foot soldiers and a fourth of lightly armed velites. The velites would start the battle with skirmishes and then retreat to form the rear-guard or be spread evenly across the other three row of infantry. I say about 4200 legionaries because according to the severity of the situation and how long the legion had been engaged in war could imply that it was more or less replenished with men, usually of the younger and less experienced classes. At the start of the campaign the legion could carry more than 4200 and by the end have rather fewer.
The first true line was therefore that of the “Hastati“, followed by the “Principes” and “Triarii” – heavily armed infantry. The lines were be made of 10 (some suggest 15) rectangular blocks of soldiers known as “manipulus“, each block set apart from the next by an open space the size of a manipulus. The manipuli of the three rows were set out as if on a chequers board so that each manipulus had an open area ahead of it.
If each manipulus was approx 18m in width and 12m in depth then we can quickly see that the width of a legion in battle formation was approximately 360m. To this we should add the fact that the velites (relatively untrained old and poor) could be distributed evenly across the armed infantry, therefore increasing their number and space required across the field of battle.
The manipulus was the smallest tactical unit within the Roman army, the soldiers within it responded to a single banner/standard. Roman flags or military standards known as “Vexillum” had almost religious value to the soldiers who would do anything to defend it.
Differently from the compact Greek phalanx formation, the Roman manipulus was able to engage in cohesive action as a single unit as well as personal hand-to-hand combat: The soldiers were set out with a broad space between one and the next, sufficient to allow them to swing and use their weapons in relative individual freedom.
A manipulus contained two “centuriae” which in the case of the Hastati and Principes consisted of 60 legionaries and of the Triarii (veterans) consisted of 30. Ie manipulus of Hastati or Principes = 120 legionaries and a manipulus of Triarii= 60 legionaries.
“Management” of these basic units involved a handful of specific roles. Each century had:
Cornicen: a trumpet player (a sort of round horn) who rang out specific orders
Signifer: a standard bearer, this was a highly important role as the Romans placed huge value on their insignia. Two men would be nominated for this role in case one fell or was unable to carry the insignia.
A Centurion: centurions who led 60 men (or 30 in the case of the Triarii) ie two of these were pulling the manipulus forward.
An Optio: another centurion who held the back and made sure no-one was falling behind. Ie two of these were making sure no-one was falling back.
Ancient Roman Cavalry: The Turmae
The cavalry was made up of elite citizens and nobility. Frequently including young men keen to make themselves known for their courage. They carried a spear, a sword, a small light round shield and no armour. They rode without stirrups but in a very ergonomic saddle which permitted them stability and mobility whilst on horseback.
Each legion would have its support of approximately 300 cavalry men subdivided into ten units of 30 men. The units in this case were called “turmae” (rather than “manipuli” for infantry). Each ten men had a “Decurion” and an “Optio” (equivalent of the centurions and optios of the manipuls) ie a turma would have 3 decuriones and 3 optios, the highest ranking of these being called a “praefectus”.
Allied troops double up the legion’s size
Allied troops provided by the “Soci” – allies of Rome – formed a wing of the legion and matched it in size, often exceeding it, in number of men and cavalry. They were headed by three Roman prefects (nominated by the Roman Consuls) who would command allied officers below them.
As opposed to the manipuls, allied troops were sub-divided into “cohorts“: 10 cohorts made a support unit of allied troops, likely composed of 400-600 men. It is likely that the cohorts would be subdivided into manipuli similar to those of the Roman legion.
The social impact of Roman legions
As outlined above, Roman legions included both Roman troops as well as those of their ‘socii’ – allied populations of Italy. Over time this came to include military capability from across the empire and soldiers of many different cultures and nationalities.
As the legions moved across vast territories and countries they brought and shared a variety of international cultures and beliefs. Over longer periods they would settle and mix with local populations. At York (Roman Eboracum), close to the northern frontier of Roman Britain, it is interesting to see the broad variety of religious artifacts and burial customs such as:
Sucellus – Celtic divinity of Agriculture and Wine (From Gaul/France)
Ocean and Tethys – Titan divinities of Greece.
The presence of these troops also meant that significant infrastructure such as drainage, roads and constructions were built for local economic stability and benefit. The tile below is stamped by the 9th Legion.
The names of Roman legions
Roman legions were initially recognised through simple numbering. As the Roman army became professional and legions were no longer disbanded and regrouped they came to have names made of name and surname – “nomina” and “cognomina” linked to aspects of their creation or situation. This naming also helped to distinguish legions which might have the same numerals for various reasons. Over time highly successful legions might even acquire several cognomina.
Legion cognomina through origins:
These legions are named through their geographical origins and likely through the greater number of soldiers from that region. Examples include:
Italica, Gallica, Macedonica, Hispana.
Legion cognomina through virtues and special exploits:
Legions were given names linked to special feats, battles or wars won include:
A particularly favoured legion of Julius Caesar in Gaul was Legio X “Equestris”, which fell in disfavour under Emperor Augustus and hence mixed with another, making it Legio X Gemina (see below).
Legion cognomina “Gemina”:
There were a considerable number of “Gemina” legions – the name means “twin” and was typically used when a legion was formed through the merger of two or more units.
Legion cognomina “Parthicae”:
This was an unnusual set of legions, whose name was based on the campaign they were meant for against the Parthian empire. Once the Parthian enemy had been vanquished they and subsequent legions which evolved from them continued to preserve their “Parthicae” name.
Military standards and flags of Roman legions:
Roman flags were known as “Vexillum”. Roman legions used a stock set of imagery for their standards: There were some 20 different standards, including animals, divinities and mythological beasts
Animals: Boar, Bull, Eagle, Elephant, Lion, She-Wolf, Stork, Two Bulls.
The famous “ninth legion” which mysteriously disappeared
A number of books have been written and films made about the ninth legion or Legio IX Hispana: It was stationed at Eboracum (York) but mysteriously disappeared off the records. Various theories have been developed to explain its disappearance.