MAIN IMPERIAL RANKS OF A ROMAN LEGIO

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:

• Contubernium (tent group): consisted of 8 men.

• 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.

• Cohors (cohort): comprised 6 centuriae.

• Legio (legion): consisted of 10 cohorts.

Main types of infantry soldiers:

• Light infantry (Velites): equipped with light arms; they hurled javelins and fired missiles with slings.

• 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.

• 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.

• 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:

• engineers

• artillerymen

• weapons instructors

• military police (frumentarii)

• carpenters

• hunters

• weapons custodians (custos armorum)

• 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:

• Aquilifer: bearer of the legionary eagle, immediately subordinate to the centurion and thus the highest-ranking among the principales;

• Campidoctor: generally a decorated veteran or an evocatus, an instructor responsible for troop training;

• Cornicularius: head of the administrative office and legionary archives, according to the rank held;

• Signifer or Vexillifer: standard-bearer (signa);

• Optio: deputy to the centurion, one for each centuria, who closed the unit’s formation;

• Medicus: including those embarked, could be a duplicarius;

• Beneficiarius: secretary to the legatus legionis or the tribunus militum, with police duties;

• Tesserarius: responsible for distributing the wooden tablet bearing the password for access to the fort;

• 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

• Centuria I – Primus Pilus prior

• Centuria II – Primus princeps prior

• Centuria III – Primus Hastatus prior

• Centuria IV – none

• Centuria V – Primus princeps posterior

• Centuria VI – Primus Hastatus posterior

Cohort II

• Centuria I – Secundus Pilus prior

• Centuria II – Secundus princeps prior

• Centuria III – Secundus Hastatus prior

• Centuria IV – Secundus Pilus posterior

• Centuria V – Secundus princeps posterior

• Centuria VI – Secundus Hastatus posterior

Cohort III

• Centuria I – Tertius Pilus prior

• Centuria II – Tertius princeps prior

• Centuria III – Tertius Hastatus prior

• Centuria IV – Tertius Pilus posterior

• Centuria V – Tertius princeps posterior

• Centuria VI – Tertius Hastatus posterior

Cohort IV

• Centuria I – Quartus Pilus prior

• Centuria II – Quartus princeps prior

• Centuria III – Quartus Hastatus prior

• Centuria IV – Quartus Pilus posterior

• Centuria V – Quartus princeps posterior

• Centuria VI – Quartus Hastatus posterior

Cohort V

• Centuria I – Quintus Pilus prior

• Centuria II – Quintus princeps prior

• Centuria III – Quintus Hastatus prior

• Centuria IV – Quintus Pilus posterior

• Centuria V – Quintus princeps posterior

• 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.

-----------------------------------------------------------------------------------------------------------------------------

THE PREFECTS

PRAEFECTUS CASTRORUM

The camp prefect was the superintendent of the camp; in the absence of the legatus and the most senior tribune, he became the commander of the legion.

PRAEFECTUS FABRUM

The praefectus fabrum was one of the field officers serving in the legions, responsible for commanding and coordinating the military engineers. This office appears to have lasted until the reign of Emperor Claudius. A praefectus fabrum could also hold, or have previously held, other military posts such as:

• centurion

• primus pilus

• tribunus militum

• praefectus castrorum

• praefectus alae

---

TRIBUNES

TRIBUNUS ANGUSTICLAVIUS

The tribunus angusticlavius was part of the legion’s command group of five tribunes. The title derived from the narrow purple stripe sewn onto the toga, indicating membership in the equestrian order. He had the right to take part in the war council but did not exercise command authority in battle. He was generally assigned to the legatus legionis.

His duties included:

• inspecting sentries,

• training recruits,

• assisting with and supervising drills,

• taking part in the war council and the legionary court,

• drawing up the rolls of soldiers,

• granting leave and passes,

• supervising supplies,

• overseeing the field hospital.

TRIBUNUS LATICLAVIUS

This post constituted the first step of the cursus honorum for senatorial families. The tribunus laticlavius was second only to the legatus legionis and superior to the other five tribuni angusticlavii (of equestrian rank) and, later, also to the praefectus castrorum. After two or three years in this military post, the young man normally returned to Rome to hold the annual magistracy of quaestor.

LEGATUS LEGIONIS

The legatus legionis was the commander of a legion. From the time of Augustus onward, the title of legatus legionis was granted to senators who commanded a legion in a province. He was subject to the supreme authority of the legatus Augusti pro praetore (governor), who was of senatorial rank.

---

THE AUXILIARY TROOPS

The auxiliary troops of the Roman army were:

• Cohors peditata: composed of 6 infantry centuriae.

• Cohors equitata: a mixed infantry and cavalry unit composed of 6 infantry centuriae plus 4 turmae (the cavalry equivalent of centuriae).

• Ala: a cavalry formation, divided into 16 turmae.

---

COHORS PEDITATA

The cohors peditata was composed of 6 infantry centuriae. The main military ranks were:

• Milites: ordinary soldiers

• Principales:

  • Cornicen (transmission of orders by sound signals)

  • Tesserarius (guard duties and passwords)

  • Signifer (standard-bearer)

  • Optio (deputy centurion)

• Centurions: commanders of the individual centuriae

• Praefectus Cohortis: commander of a cohors peditata

---

COHORS EQUITATA

This cohort was a mixed infantry and cavalry unit composed of 6 infantry centuriae plus 4 cavalry turmae. The main military ranks for the infantry component were the same as those described for the cohors peditata. For the cavalry component, the ranks were as follows:

• ordinary cavalrymen

• Sesquiplicarius (with a specialist role)

• Duplicarius (deputy decurion)

• Decurion (commander of a turma)

• Praefectus Cohortis (commander of a cohors equitata)

---

ALA

The ala was one of the two cavalry formations that flanked the legion’s battle line. A cavalry ala was composed of 500 horsemen, divided into 16 turmae of 32 men each, each commanded by a decurion. The two alae together numbered 1,000 men, 2 praefecti alae, and 32 decurions.

The main military ranks in each ala were:

• ordinary cavalrymen

• Sesquiplicarius (with a specialist role, such as the Speculator, a scout)

• Duplicarius (deputy decurion)

• Decurion (commander of a turma)

• Prefect of the ala or Prefect of cavalry (commander of a cavalry ala)

-----------------------------------------------------------------------------------------------------------------------------