Legion Organization

The Marian legion originally consisted of 60 centuries organized into ten cohorts broken down as follows:

  • Each Century was composed of 10 contuburnia of 6-8 men. These soldiers ate, trained, bunked, laboured and fought together. They shared a mule and a tent on the march.
  • Centuries were paired into administrative units known as maniples; the senior was identified as the prior century and the junior as posterior.
  • Each Cohort contained three maniples ranked on a seniority basis (Pilus first followed by Princeps and then Hastatus).
  • Legion cohorts numbered 1 through 9 featured 6 centuries each. Marius may have been responsible for reducing the number of centuries in the 1st cohort from six to five. By the mid-1st century AD the first cohort centuries were doubled in size.
  • A small cavalry contingent of 120 men (4 turmae of 30 horsemen) was attached to each legion. They were employed as scouts and messengers. Each cohort was assigned 10 cavalrymen and 20 were dedicated to the HQ (principia).


The roman army had three ranks – Officers, Centurions and Lower Ranks


Legatus Legionis

  • The legati Augusti legionis (legionary commanders) were senators, ex-praetors around thirty years of age who typically served a 3 (sometimes up to 7) year tour of duty.
  • Legati Augusti propraetore governed Imperial provinces. Those provinces with one legion were commanded by ex-praetors (who also acted as legionary COs) and those with more by ex-consuls. The latter commanded all of the provincial legates and their troops (i.e., Britain had four legions).

Tribunus Laticlavius

  • The second-in-command, a tribune and a senatorial designate around the age of 25, served for one year. Although command technically defaulted to the Tribunus Laticlavius in the absence of the Legatus, it is more probable that the Praefectus and the Tribuni Angusticlavii (see below) assumed control.

Tribuni Angusticlavii

  • Each legion had five  equestrian tribunes (Tribuni Angusticlavii,) who served 3-4 years and then assumed command of a cavalry ala. They were generally former magistrates and/or auxiliary cohors peditata/equitata commanders. During the Principate they occupied staff positions with an administrative/judicial focus.
  • Tacitus reported that they monitored the performance/reliability of the centurions. Their staff (officium) was comprised of clerks (cornicularii and secutores) without military responsibilities who recorded casualties, maintained current lists of men serving, processed furlough applications and dispensed discharges to retiring veterans. Tribunes often commanded vexillations, detachments of one or more cohorts on special assignments.
  • Tribuni Semestres were part of H.Q. staff and served 6 months before resuming civilian life. Following the Flavian era they commanded the legion’s 120 man cavalry contingent. The cavalrymen were ranked as non-combatants along with the headquarters staff and were attached to specific centuries (as opposed to forming individual units).

Praefectus Castrorum

  • The third-in-command was an equestrian, a former head centurion in his late 50s with 30 plus years of experience. He was basically a quartermaster responsible for choosing camp sites and overseeing their construction inclusive of entrenchments. He inspected tent lines in temporary camps. During war he supervised the legion’s baggage train, and if siege operations were anticipated he managed the battering rams and ammunition supplies. In permanent installations he oversaw the construction of barracks-blocks, internal buildings, wells and aqueducts.
  • He was the officer in command of the doctors (medici), the surveyors (mensores) and the horologiarius, the man responsible for the camp clock. He oversaw the supply of construction and surveying equipment, furnishings, fabrica supplies (inclusive of wood, iron and coal) and medical equipment for the legion’s hospital (valetudinarium).

Primus Pilus

  • The fourth-in-command was the senior centurion and leader of the 1st century of the 1st cohort. He held his post for one year. Parker believes that there were two primi pili, one who commanded the troops of the first cohort and one who served in the Legion’s headquarters.


  • The centurion commanding the second century of the first cohort was next in line, and he was responsible for the headquarters’ staff as well as training. Ranked below him were the remaining centurions of the first cohort in the following order – hastatus, princeps posterior and hastatus posterior.

THE CENTURIONATE AND RANKS BELOW (first and second centuries AD)


He carried the legion’s gilded eagle (the original under Marius was silver) and ranked just below a centurion. He was entrusted with the legion’s pay chest.



Centurions in cohorts 2-9 were equal in rank with seniority determined by years of service. They were recognized by their transverse helmet crest, sword worn on the left and a swagger stick (vitus) with which they dispensed discipline. They typically rode when a legion was on the march. Centurions tended to die in service as opposed to retiring to civilian life.

Principales and Immunes

Below the rank of centurion men were designated as either principales or immunes. The optio, signifer and tesserarius were principales who assisted centurions and were exempt from normal fatigues. Immunes, men who were excused from regular fatigues by virtue of special skills (blacksmiths, carpenters, surveyors, medical assistants, etc.), comprised almost 20% of each unit.


The standard bearer handled the paperwork at century level. Vegetius says that the garrison was managed by the signiferi who were directly responsible for finances. They recorded financial transactions, issued receipts, documented account activity and dispensed pay.


He was a chosen man, a centurion-in-training who assumed field command if the unit’s centurion was incapacitated or killed. He carried a staff of office known as a hastile.


The tesserarius controlled the daily watchword and was responsible for sentries and other fatigues.

Custos Armorum

He was responsible for centurial equipment, repairs, and weapons.


Each contubernium was commanded by a decanus.


The basic foot soldier served for 20-25 years (depending upon the time period).