Roman Cohort

A cohort (Latin cohors) was a major subdivision of a Roman legion made up of several centuries. In the standard organisation of the Principate, a legion had ten cohorts; a normal cohort contained six centuries, while the first cohort had special status and could be larger.

In brief:

• a cohort was larger than a century and smaller than a legion;
• a normal Principate cohort had an establishment of about 480 legionaries;
• actual strength varied with period, losses and replacements.

The figures are a comparative establishment, not a permanent headcount. Ancient units rarely remained at full strength throughout a campaign.

Composition and Strength

The cohort organisation developed in the late Republic from the earlier manipular system. Two centuries formed a manipule and three maniples a cohort; when the cohort became the principal tactical subdivision, traditional century titles and grades of seniority survived.

For a normal imperial cohort, historians often use six centuries of about 80 legionaries, or roughly 480 heavy infantry. The first cohort guarded the legionary eagle, contained the senior centurions and, in some periods, had enlarged centuries. Exact arrangements changed, so figures such as 480, 800 or 960 should be understood as reconstructed establishments rather than a universal size for every cohort.

The Cohort in Battle

A cohort was large enough to receive a distinct mission yet compact enough to manoeuvre within the legion. A commander could deploy cohorts in several lines, keep some in reserve, reinforce a flank or assign them to an assault. The arrangement depended on terrain and plan rather than on one unchanging pattern of five cohorts in front and five behind.

Within the cohort, centurions controlled their centuries and the senior officer coordinated their action. Cohort organisation allowed a legion to divide into detachments while retaining command and to operate on broken ground more flexibly than a single undivided mass.

Legionary, Auxiliary and Urban Cohorts

The word cohors was not limited to legionary subdivisions. The auxilia included infantry cohorts and mixed cohors equitata. The labels quingenaria and milliaria indicated nominal strength classes, but did not mean that exactly 500 or 1,000 personnel were always present.

The Praetorian Guard, the urban cohorts and the cohortes vigilum of Rome also used the term. Their duties, recruitment and command differed from those of a legionary cohort, so a shared name does not prove identical organisation.

FAQ

How many centuries were in a cohort? A normal Principate cohort had six. The first cohort had a special organisation that changed over time.

How many soldiers were in a Roman cohort? About 480 is a common establishment for a normal legionary cohort. Actual strength could be substantially lower.

Did cohorts exist only in legions? No. Cohorts also served in the auxilia, Praetorian Guard and urban services, but their organisation differed.

Related Topics

• Roman legion
• Century
• Contubernium
• Centurion
• Auxilia

Literature

• Polybius. The Histories, Book VI.

• Caesar. The Gallic War.

• Goldsworthy, Adrian. The Complete Roman Army. London, 2003.