The Imperial Roman Legion

Under Augustus, the Imperial Roman legion became a permanent unit of about 5,200 heavy infantry, staffed by entirely professional soldiers on standard 25-year terms. He also fixed the number of legions at 28, having inherited over 50 after his defeat of Mark Anthony, although 3 were destroyed in the Varian Disaster. Under Septimius Severus, this number had grown to 30 legions of 5,600 heavy infantry.


A legion was divided into ten cohorts, each of six centuries, with a small force of cavalry (eques legionis) attached to it used as messengers and scouts.

The Organisation of an Imperial Legion. (c) romanoimpero

The cohort (cohors) was made up of 480 men in 6 centuries, with the first century being double-strength. The century (centuria) was made up of 80 men in 10 contubernia, or tent-groups. The contubernium was made up of 8 men.

The legion was commanded by a Legionary Legate (legatus legionis), supported by a Broad-Stripe Tribune (tribunus laticlavius), 5 Narrow-Stripe Tribunes (tribuni angusticlavii) and a Camp Prefect (praefectus castrorum). Each cohort and century was commanded by a centurion (centurio), with an optio as his second in command.

See Ranks of the Roman Army for more detail.

A legion was always supported by the Auxilia, non-citizen units, who normally matched the legion in strength.


A legionary was expected to carry a great deal of equipment with him whilst on campaign; not only his weapons and armour but also his clothes, cooking utensils and tools for camp construction.

He was armed with a gladius, a pugio and two pila, while wearing a galea and lorica segmentata and carrying a scutum.

Aside from the weapons and armour, a legionary would carry such items as a pickaxe, a saw, a sickle, a shovel, a waterskin, a wicker basket and more, which would have been carried on a forked pole. This was first introduced by the concsul C. Marius in 107 BC and earned his men the nickname Marius’ Mules.

See Equipment of the Roman Army for more detail.

An illustration of the Roman Army on the march. (c) Radu Oltean

List of Imperial Legions

I Adiutrix
I Germanica
I Italica
I Minervia
I Parthica
II Adiutrix
II Augusta
II Italica
II Parthica
II Traiana Fortis
III Augusta
III Cyrenaica
III Gallica
III Italica
III Parthica
IV Flavia Felix
IV Macedonica
IV Scythica
V Alaudae
V Macedonica
VI Ferrata
VI Victrix
VII Claudia
VII Gemina
VIII Augusta
IX Hispana
X Fretensis
X Gemina
XI Claudia
XII Fulminata
XIII Gemina
XIV Gemina
XV Apollinaris
XV Primigenia
XVI Flavia Firma
XVI Gallica
XX Valeria Victrix
XXI Rapax
XXII Deiotariana
XXII Primigenia
XXX Ulpia Victrix

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