Cohort (military unit)

Military organization
Latvian platoon at Camp Lejune.jpg
Typical Units Typical numbers Typical Commander
Fireteam 2–4 Lance Corporal /
8–14 Corporal/
Staff Sergeant
15–45 Second Lieutenant /
First Lieutenant /
80–150 Captain /
Battalion /
300–800 Lieutenant Colonel
Regiment /
Brigade /
1,000–5,500 Colonel /
Brigadier General
Division 10,000–25,000 Major General
Corps 30,000–50,000 Lieutenant General
Field Army 100,000–300,000 General
Army Group /
2+ field armies Field Marshal /
Five-star General
Region /
4+ army groups Six-star rank /

A cohort (from the Latin cohors, plural cohortes, see wikt:cohors for full inflection table) was a standard tactical military unit of a Roman legion, though the standard changed with time and situation, and was composed of between 360-800 soldiers.[citation needed] A cohort is considered to be the equivalent of a modern military battalion. The cohort replaced the maniple following the reforms attributed to Gaius Marius in 107 BC. Shortly after the military reforms of Marius, each Legion formed 10 cohorts. The cohort was named "The First Cohort," "The Second Cohort,"... The First Cohort gathered the most experienced legionaries, while the legionaries in the Tenth Cohort were the least experienced. Until the middle of the third century AD, 10 cohorts (about 5000 men total) made up a Roman legion.

Legionary cohort[]

Originally, a cohort consisted of six centuriae, each commanded by a centurion assisted by junior officers. At various times prior to the reforms, a century might have 60 to 100 men. The cohort had no permanent commander; it is assumed that in combat, the most senior centurion of the six would have commanded the entire cohort.[citation needed] In order of seniority, the six centurions were titled hastatus posterior, hastatus prior, princeps posterior, princeps prior, pilus posterior and pilus prior (most senior).

During the reforms in the 1st century AD, the command structure and make-up of the legions was formally laid down, in a form that would endure for centuries. Standard centuriae consisted of 80 men each. The first cohort was made up of five double-strength centuries totalling 800 men, the centurion of its 1st century automatically being the most senior in the legion. This century was known as the primus pilii (first files), and its centurion was known as the primus pilus (first file or first spear). The Primus Pilus could be promoted to Praefectus Castrorum, or "Camp Prefect." The Praefectus Castrorum would be in charge of the daily running of a legion.

These ranks followed the order of seniority in the earlier manipular legions, where the youngest and least experienced units were termed hastati, next principes, and the oldest and most experienced triarii (pilus was a rare alternative name for triarius, the singular of triarii)[citation needed].

The reformed legion numbered about 5,400 men, including officers, engineers and usually a small unit of cavalry (equites legionis; 120 men plus horses).[1]

Types of cohort[]

Denarius, struck under Mark Antony in honor of the 'Cohors Speculatorum'

Other Roman cohorts[]

Some paramilitary corps in Rome consisted of one or more cohorts, though none were part of a legion:

Furthermore, the Latin word cohors was used in a looser way to describe a rather large "company" of people (see, for instance, cohors amicorum).

See also[]


  1. ^ Goldsworthy, Adrian (2003). The Complete Roman Army. London: Thames & Hudson Ltd. ISBN 0-500-05124-0.
  2. ^ "Hence adj. Pălātīnus -a -um Palatine; Apollo, whose temple was on the Palatine, Hor.; also relating to the imperial palace, imperial: Ov."—Simpson, D. P. (1968). Cassell's Latin Dictionary (5th ed.). New York: Macmillan General Reference. p. 420. ISBN 0-02-522570-7.

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