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Structure of early Imperial Roman army

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Roman legionnaires
Roman legionaries

The Roman Legion (legio) was organized to ensure maximum efficiency not only at the level of the entire legion, but also at its individual units. To this end, a strict command structure and precise division into individual units was created, which was largely due to the long evolution of the Roman army throughout history.

Below are presented the next units from the lowest level, to command in the Roman legion.


The smallest unit located at the very bottom of the legion structure was contubernium group of 8 soldiers (milites or munifex), who shared the same tent, ate, slept and fought together. The Contubernium had its own draft animal to carry supplies that they themselves could not carry.

Informally in contubernium there was also a division into pairs, where one of the legionaries supported the other (e.g. in the event of his death he notified his family or tried to ensure his dignified burial).

New recruits (tirones) needed about 6 months to become full-fledged milites. During this time they had low regard among comrades in arms.

The head of contubernium was decanus, whose name suggests that he commanded 10 people. In practice, in addition to 8 legionaries, the contubernium consisted of 2 slaves or helpers who supported soldiers in their daily duties, such as cooking, guarding pack animals or caring for equipment. One of his companions, chosen by his colleagues, became the commander of contubernium. Most often he was the most experienced legionary. It is worth mentioning that during the battle it had no significance from the command point of view.

Life of a Roman legionary


The century was a legion unit composed of 80 legionaries – 10 contubernia. The name itself – suggesting “a hundred” is due to the fact that – again – each sub-unit had 2 civilians, who in total counted 20 people in centuria. Together, officially, the centuria numbered 100 people. However, 80 legionaries took part in the fight.

The command over the centurion was held by centurion (centurio), an officer who was appointed by a higher command. Most often he was an experienced and distinguished legionary. His deputy was optio, who helped maintain discipline in centuria and conduct daily training. The centurion was in the front line of the unit during the battle when optio was guarding troops from the back on the opposite side. The Centurion was thus involved in direct combat, commanding combat and being in constant danger; optio, in turn, took care of formation, maintaining discipline and prevented escapes. In the event of the death of a centurion, he assumed command of the centurion.

The centuria also included:

  • signifer – ensign carrying signum, i.e. a military banner with the emblem of a given unit
  • cornicen – trumpeter
  • tesserarius – soldier responsible for the guards


Cohort (cohors) was a tactical unit of 6 centuries, with a total of 480 legionaries. There were 10 cohorts in the legion. During the battle, the commander manoeuvred a cohort to support a particular sector of the battlefield. Each of the cohorts had its own unique sound signal, which enabled agile command without sending orders through emissaries.

Cohort command was in the hands of the most experienced centurion out of six who were in the cohort. Naturally, the oldest rank still commanded his centurion, and the other centurions were his advisers. Names of subsequent centurions, in order of importance: pilus prior, pilus posterior, princeps prior, princeps posterior, hastatus prior and hastatus posterior.

The first cohort in numbering was the elite of the legion. For this reason, it consisted of 5 double centuriae – or 800 people (160 x 5 centuriae). The centurions in this cohort were the most important centurions in the legion. This cohort had the honour of guarding the legionary eagle (aquila), which he wore aquilifer, and officially took care of the safety of the commander.

The first cohort was headed by the tallest primus pilus (“first spear”), the most experienced centurion among the 5 centurions in the first cohort, and thus the most important soldier in the legion. He had the right to participate in staff talks and present his military recommendations and reservations of soldiers. If the ordinary legionary had an entire legion case, he would first go to the centurion under whom he served; he then informed primus pilus, who in turn referred the case to the commander.

Struktura rzymskiego legionu okresu wczesnego cesarstwa


Order of command in the Roman legion:

  1. Legate (legatus) – legion commander, a senator appointed for a given period by the emperor.
  2. Military tribune – this was a position in the legion due to political reasons. Becoming a tribunal in the army allowed a young Roman to begin his political career, who wanted to climb the cursus honorum and belonged to a family in which one of the family members sat in the senate. There were 6 military tribunes in the legion, who in republican times exchanged their powers and thus gained experience. During the empire, five tribunes (tribuni angusticlavii) served more as secretaries and officials in the legion of the legion. The sixth tribune (tribunus laticlavius ​​) had an exceptionally strong position because of the importance of his family. This guaranteed him a second place in the legion, in the context of the command, and direct participation in the fighting.
  3. Prefect of the camp (praefectus castrorum) – the officer responsible for supplying the legion, setting out the camp and its management. Most often this position was taken by the former primus pilus,, which was the highest possible position a soldier in the Roman legion could have taken. The prefect was appointed by the legion commander.
  4. Primus pilus – (“first spear”), the most experienced centurion among the 5 centurions in the first cohort, and thus the most important soldier in the legion

In total, the Roman legion had 5248 people in full strength, including 5,120 heavy infantry and 128 cavalry (equites). In practice, however, the number was lower – e.g. during the campaign Germanicus in Germania, the legion had between 3,000 and 5,000 soldiers. There were a total of 59 optiones and 59 centurions in the legion. What’s more, each legion had a certain number of military and siege engines (ballists, catapults, scorpions), and civilians were engineers, architects, medics (so-called immunes). Legionaries were often accompanied by legionary families and merchants.

In the event of the destruction of the entire legion, its numbering was no longer used. A great example are the legions of the XVII, XVIII and XIX, which were broken up in the battle in the Teutoburg Forest (9 CE), and whose numbering was never used again.

  • Ludwig Dyck, The Roman Barbarian Wars: The Era of Roman Conquest
  • Stephen Dando-Collins, Legions of Rome
  • Adrian Goldsworthy, THe Roman Army at War 100 BC - 200 AD

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