Cohort (cohors; plural cohortes) was a tactical unit of the Roman army with 3 maniple, so 6 centuries. Quantitative equivalent of the modern battalion.
The legio had ten cohorts. At the time of Julius Caesar, there were 600 people in the unit. The names of the cohorts were not complicated: “first cohort”, “second cohort” etc. During the Roman Empire first cohort of legio – cohors miliaria – had 800 soldiers (5 centuries, 160 soldiers); others – cohortes quingenariae – each 480 (6 centuries, 80 soldiers). The cohorts did not normally have their own commander, but were commanded by the highest centurion in battle. The first cohort was commanded by primus pilus (the highest-ranking centurion in the legio). This cohort wielded the banner and eagle of the legio during the fight, making it the most experienced and prestigious unit. The number and importance of the first cohort increased in the first century CE.
Centurions of the next six centuries (from the least to the most prestigious position): hastatus posterior, hastatus prior, princeps posterior, princeps prior, pilus posterior and pilus prior.
The cohort most often had about 480 soldiers. Each of the sixth centuries (centuriae) consisted of 80 people, where each was commanded by a centurion, assisted by a junior officer. Centuria has counted from 60 to 80 people throughout history.
The cohort as a tactical unit was the result of Marius’ reforms carried out around 108 BCE. It abolished the handling system and the division of legionaires into hastati, principes and triarii (although in the Roman nomenclature these names remained, but they simply meant individual, identically equipped cohorts). Along with the abolition of the “classes” of soldiers, the armaments were unified.
It is worth noting that the first mention of the cohort appears in Polibius accounts, and relates to the wars in Spain conducted by Scipio Africanus during Second Punic War. This mention shows that the concept of greater tactical relationships than manipul was previously known, but all historians agree that it was a one-off operation.
Types of Roman cohorts
- Cohors alaria – an allied or auxilia unit
- Cohors classica – auxlia unit originally formed from marines
- Cohors equitata – auxilia infantry unit with a mounted squadron
- Cohors peditata – infantry unit
- Cohors sagittaria – unit of archers
- Cohors speculatorum – guard unit of Mark Antony, composed of scouts
- Cohors torquata – auxilia unit awarded with torques (military decoration)
- Cohors tumultuaria (from tumultus – “chaos”) – irregular auxilia unit
The auxilia cohorts could be quinquagenaria (i.e. nominally 500 soldiers) or milliaria (1000 people).
Other Roman cohorts
There were also paramilitary cohorts in Rome that did not belong to the legio:
- Nine Praetorian Cohorts (cohortes praetoriae).
- Cohors togata – a unit of praetorians dressed “in civilian”, performing their duties inside the holy center of Rome (pomperium), where armed forces could not stay.
- Cohortes urbanae – “city cohorts”; militia patrolling the capital.
- Cohortes vigilum – vigiles; law enforcement, militia and fire brigade.
- Cohors Germanorum – unit of the Emperor’s Germanic guard (Germani custodes corporis)