Cohort (military unit)
A cohort was the basic tactical unit of a Roman legion
Roman legion
A Roman legion normally indicates the basic ancient Roman army unit recruited specifically from Roman citizens. The organization of legions varied greatly over time but they were typically composed of perhaps 5,000 soldiers, divided into maniples and later into "cohorts"...

 following the reforms
Marian reforms
The Marian reforms of 107 BC were a group of military reforms initiated by Gaius Marius, a statesman and general of the Roman republic.- Roman army before the Marian reforms :...

 of Gaius Marius
Gaius Marius
Gaius Marius was a Roman general and statesman. He was elected consul an unprecedented seven times during his career. He was also noted for his dramatic reforms of Roman armies, authorizing recruitment of landless citizens, eliminating the manipular military formations, and reorganizing the...

 in 107 BC.

Legionary cohort

Immediately after the Marian reforms, a Roman legion comprised ten cohorts, known simply as "The first cohort", "The second cohort" etc. The first cohort was considered to be the most senior and prestigious, and the tenth the least.

A cohort consisted of six "centuries" or centuria  of 80 men, each commanded by a centurion
A centurion was a professional officer of the Roman army .Centurion may also refer to:-Military:* Centurion tank, British battle tank* HMS Centurion, name of several ships and a shore base of the British Royal Navy...

 assisted by junior officers. At various times prior to the reforms, a century might have meant a unit of 60, 80 or 100 men. It is almost certain that the most senior centurion of the six would have commanded the entire cohort. In order of seniority, the six centurions were titled hastatus posterior, hastatus prior, princeps posterior, princeps prior, pilus posterior and pilus prior (most senior). This followed the order of seniority in the earlier legions, where the youngest and least experienced units were termed hastati
Hastatii were a class of infantry in the armies of the early Roman Republic who originally fought as spearmen, and later as swordsmen. They were originally some of the poorest men in the legion, and could afford only modest equipment — light armour and a large shield, in their service as the...

, next principes
Principes were spearmen, and later swordsmen, in the armies of the early Roman Republic. They were men in the prime of their lives who were fairly wealthy, and could afford decent equipment. They were the heavier infantry of the legion who carried large shields and wore good quality armour. Their...

, and the oldest and most experienced triarii
Triarii were one of the elements of the early Roman military Manipular legions of the early Roman Republic . They were the oldest and among the wealthiest men in the army, and could afford good quality equipment. They wore heavy metal armour and carried large shields, their usual position being...

 (pilus was an alternative name for triarius, the singular of triarii).

During the first century AD, the command structure and make-up of the legions was formally laid down, in a form that would endure for centuries. The first cohort was now made up of five double-strength centuries totalling 800 men, the centurion of its first century automatically being the most senior in the legion: the primus pilus or "first file". (pilus meant file whilst pilum meant spear.)

The legion at this time numbered about 5,400 men, including officers, engineers and usually a small unit of cavalry (equites; 120 men and horses).

Types of cohort

Auxiliary cohorts could be quingenaria (nominally 500 strong) or milliaria (1000 strong).
  • Cohors alaria: allied or auxiliary unit.
  • Cohors classica: auxiliary unit originally formed of sailors and marines.
  • Cohors equitata (LA): unit of auxiliary infantry with attached mounted squadrons.
  • Cohors peditata (LA): infantry unit.
  • Cohors sagittaria: infantry auxiliary unit of bowmen.
  • Cohors speculatorum (LA): guard unit of Mark Antony
    Mark Antony
    Marcus Antonius , known in English as Mark Antony, was a Roman politician and general. As a military commander and administrator, he was an important supporter and loyal friend of his mother's cousin Julius Caesar...

     composed of scouts.
  • Cohors torquata (LA): auxiliary unit granted a torques (military decoration).
  • Cohors tumultuaria (from tumultus, "chaos"): irregular
    Irregular military
    Irregular military refers to any non-standard military. Being defined by exclusion, there is significant variance in what comes under the term. It can refer to the type of military organization, or to the type of tactics used....

     auxiliary unit.

Other Roman cohorts

Some paramilitary corps in Rome consisted of one or more cohorts, though none were part of a legion:
  • The nine cohortes praetoriae, never grouped to a legion, the famous and infamous Praetorians
    Praetorian Guard
    The Praetorian Guard was a force of bodyguards used by Roman Emperors. The title was already used during the Roman Republic for the guards of Roman generals, at least since the rise to prominence of the Scipio family around 275 BC...

    . The term was first used to refer to the bodyguard of a general during the Republic
    Roman Republic
    The Roman Republic was the period of the ancient Roman civilization where the government operated as a republic. It began with the overthrow of the Roman monarchy, traditionally dated around 508 BC, and its replacement by a government headed by two consuls, elected annually by the citizens and...

    ; later, a unit of Imperial guards (temporarily restyled cohors palatina, "Imperial Cohort", circa 300 AD
    Year 300 was a leap year starting on Monday of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantius and Valerius...

    , under Diocletian
    Diocletian |latinized]] upon his accession to Diocletian . c. 22 December 244  – 3 December 311), was a Roman Emperor from 284 to 305....

    's tetrarchy
    The term Tetrarchy describes any system of government where power is divided among four individuals, but usually refers to the tetrarchy instituted by Roman Emperor Diocletian in 293, marking the end of the Crisis of the Third Century and the recovery of the Roman Empire...

    • Cohors togata was a unit of the Praetorian guard in civilian dress tasked with duties within the pomerium
      The pomerium or pomoerium , was the sacred boundary of the city of Rome. In legal terms, Rome existed only within the pomerium; everything beyond it was simply territory belonging to Rome.-Location and extensions:Tradition maintained that it was the original line ploughed by Romulus around the...

       (sacred center of the Capital, where all armed forces were forbidden).
  • Cohortes urbanae
    Cohortes urbanae
    The cohortes urbanae of ancient Rome were created by Augustus to counterbalance the enormous power of the Praetorian Guard in the city of Rome and serve as a police force...

    , "urban cohort": military police unit patrolling in the capital.
  • Cohortes vigilum, "watchmen"; unit of the police force annex fire brigade in the capital.
  • Cohors Germanorum (LA): the unit of Germani custodes corporis (imperial body guards recruited in Germania
    Germania was the Greek and Roman geographical term for the geographical regions inhabited by mainly by peoples considered to be Germani. It was most often used to refer especially to the east of the Rhine and north of the Danube...


Furthermore, the Latin word cohors was used in a looser way to describe a rather large "company" of people (see, for instance, cohors amicorum
Cohors amicorum
Cohors amicorum is a Latin term, literally meaning "cohort of friends". The notion cohort is to be taken not in the strict, military sense , but indicated a fairly large number; accordingly, friend is to be taken in a loose sense, rather as in amicus curiae, compare the Hellenistic Aulic title philos...

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