The basic structure of the Roman army in its classical imperial period (27 BC–AD 180) was composed of legions and auxiliary troops. The legion was made up of Roman citizens, while the auxiliary troops consisted of soldiers drawn from peoples previously conquered by Rome but not yet granted Roman citizenship (cavalry alae; infantry cohorts; mixed cohorts of infantry and cavalry).
THE ROMAN LEGION
Its basic structures were as follows:
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Contubernium (tent group): consisted of 8 men.
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Centuria (century): was made up of 10 contubernia, for a total of 80 men, commanded by a centurion. Centuriae were paired to form a manipulus. Each centuria consisted of approximately 69 ordinary soldiers; 5–6 immunes; 4 principales (Optio, Signifer, Tesserarius, Cornicen); and 1 centurion.
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Cohors (cohort): comprised 6 centuriae.
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Legio (legion): consisted of 10 cohorts.
Main types of infantry soldiers:
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Light infantry (Velites): equipped with light arms; they hurled javelins and fired missiles with slings.
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Heavy infantry (Principes): armed with the pilum as a throwing weapon, helmet, shield, and gladius.
EACH LEGION INCLUDED THE FOLLOWING MILITARY RANKS:
RECRUITS
They had to learn the conduct expected of them as members of the legion and become familiar with equipment and weapons. They had to learn and train in combat techniques.
MILITES (sing. MILES)
Legionaries were not only the core of the legion’s fighting force but were also employed in numerous construction and engineering works. Roman roads—many of which still exist today—are an example of legionary engineering.
They had to continue training and improving their skills.
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Miles Sagittarius: the sagittarii were Roman soldiers employed both as cavalry units and as infantry. After the Augustan reform, auxiliary units were newly trained or recruited. The shooting of these archers was powerful and accurate.
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Miles Funditor: the slinger was a light infantryman who used a sling capable of hurling projectiles (stone, clay, or lead) up to 400 meters. In antiquity, the most famous slingers were the Rhodians (from the island of Rhodes) and above all the inhabitants of the Balearic Islands, widely employed as mercenaries by the Romans, to the point that entire cohorts of slingers were formed.
IMMUNES (sing. IMMUNIS)
The immunes were legionaries of higher status than the ordinary soldier, as they possessed specialist skills that allowed them to perform duties not common to other soldiers. These skills exempted them from the most arduous and dangerous tasks, such as digging ditches or patrolling ramparts. In general, the immunes included:
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engineers
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artillerymen
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weapons instructors
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military police (frumentarii)
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carpenters
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hunters
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weapons custodians (custos armorum)
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administrative officials: curator and librarius
Librarius Legionis: a legionary assigned to special administrative duties within the legion. He could be responsible for recording incoming and outgoing supplies, monitoring soldiers’ savings deposited at the principia of the camp, or recording deaths occurring during military service.
Curator Legionis: the officer responsible for the legion’s supplies, particularly those sent from Rome, especially grain. The curator had to measure and package the grain in sacks of seed (which kept longer than flour) for distribution in the camp.
PRINCIPALES
The principales were the non-commissioned officers or junior officers of the Roman legion. They included:
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Aquilifer: bearer of the legionary eagle, immediately subordinate to the centurion and thus the highest-ranking among the principales;
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Campidoctor: generally a decorated veteran or an evocatus, an instructor responsible for troop training;
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Cornicularius: head of the administrative office and legionary archives, according to the rank held;
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Signifer or Vexillifer: standard-bearer (signa);
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Optio: deputy to the centurion, one for each centuria, who closed the unit’s formation;
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Medicus: including those embarked, could be a duplicarius;
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Beneficiarius: secretary to the legatus legionis or the tribunus militum, with police duties;
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Tesserarius: responsible for distributing the wooden tablet bearing the password for access to the fort;
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Evocatus: a soldier retained in service or recalled beyond the legal term because of high qualifications in administration, policing, construction and engineering works, or in supply and training sectors.
Decanus: was responsible for a group of 8 soldiers (milites or immunes).
The military roles in the preceding list shown in bold received double pay compared to ordinary soldiers (milites); for this reason they were called duplicarii.
CENTURIONES (OFFICERS)
CENTURIONES (sing. CENTURIO)
They had direct command of a centuria of the legion. Each centuria was paired with another to form a manipulus. In each manipulus there was a “front” centurion (prior) and a “rear” centurion (posterior).
The centurions were divided as follows:
Cohort I
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Centuria I – Primus Pilus prior
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Centuria II – Primus princeps prior
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Centuria III – Primus Hastatus prior
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Centuria IV – none
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Centuria V – Primus princeps posterior
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Centuria VI – Primus Hastatus posterior
Cohort II
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Centuria I – Secundus Pilus prior
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Centuria II – Secundus princeps prior
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Centuria III – Secundus Hastatus prior
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Centuria IV – Secundus Pilus posterior
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Centuria V – Secundus princeps posterior
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Centuria VI – Secundus Hastatus posterior
Cohort III
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Centuria I – Tertius Pilus prior
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Centuria II – Tertius princeps prior
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Centuria III – Tertius Hastatus prior
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Centuria IV – Tertius Pilus posterior
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Centuria V – Tertius princeps posterior
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Centuria VI – Tertius Hastatus posterior
Cohort IV
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Centuria I – Quartus Pilus prior
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Centuria II – Quartus princeps prior
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Centuria III – Quartus Hastatus prior
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Centuria IV – Quartus Pilus posterior
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Centuria V – Quartus princeps posterior
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Centuria VI – Quartus Hastatus posterior
Cohort V
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Centuria I – Quintus Pilus prior
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Centuria II – Quintus princeps prior
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Centuria III – Quintus Hastatus prior
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Centuria IV – Quintus Pilus posterior
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Centuria V – Quintus princeps posterior
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Centuria VI – Quintus Hastatus posterior
The same scheme applied to the centurions of cohorts VI, VII, VIII, IX, and X.
A legion numbered 59 centurions (5 in the I cohort + 54 in the other cohorts).
PRIMUS PILUS
He commanded Centuria I of the I Cohort and was the most senior centurion of the entire legion. He was the only centurion granted access to the legion’s war council.