Roman Army

The Roman army was Rome's armed force from the early citizen militia to the professional legions of the Principate and the Late Roman armies of the Dominate. It included legions, allied and auxiliary troops, the fleet, engineers, baggage trains, command staffs and a developed system of military camps.

In brief:

• the main unit of the classic army was the legion;
• a legion was divided into cohorts, centuries and contubernia;
• auxiliaries, cavalry, the fleet and specialists served alongside the legions;
• the army's strength rested not only on weapons, but also on discipline, roads, camps, supply and provincial administration.

Legionnaires of Legio X Fretensis. Reconstruction

Army structure

Under the Principate the Roman army was built around legions and auxiliaries. A legion was a heavy infantry formation of citizens; its soldiers were legionaries. Inside the legion the main levels were the contubernium, century and cohort. They were commanded by decani, centurions, tribunes and a legate.

The auxilia supplemented the legions with cavalry, light infantry, archers, slingers and specialized contingents. After service many auxiliaries received Roman citizenship. Alongside the land forces, the navy protected communications, transport and river frontiers.

Command and ranks

The command system combined political and professional elements. A legion was usually led by a legate, while everyday discipline and combat training depended heavily on the centurions. Within a century the optio, tesserarius and other junior officers played important roles. Standard-bearers — aquilifer, signifer, imaginifer and vexillarius — guarded the military standards and the sacred identity of the unit.

Special units such as the Praetorians had political importance because they stood close to the emperor. In the Late Empire the structure changed: field armies, frontier troops, comitatenses, limitanei and new command posts appeared.

Equipment, camps and supply

The Roman army is often associated with the gladius, pilum, scutum and armour such as lorica segmentata, hamata, squamata and helmets. In practice, equipment depended on period, region, unit type and supply.

Infrastructure mattered just as much. The castrum allowed the army to create a protected camp quickly, roads accelerated marching and supply, and engineers built bridges, fortifications and siege engines. The Roman army was therefore not only a fighting force, but also an instrument of construction, territorial control and the Romanization of provinces.

Periods of development

I. Republic The early army was a citizen militia. During the Republic, manipular tactics and allied contingents developed, followed by the professionalization of the late Republic and reforms associated with Gaius Marius.

II. Principate After Augustus, the legions became a permanent professional army stationed on the frontiers of the empire. They were supported by auxiliaries, the fleet and a network of military camps.

III. Late Empire After the third-century crisis the army became more fragmented and flexible. For soldiers of this period, see Soldiers of the Roman Empire in the Dominate.

Topic navigation

I. Organization

• Legion
• List of Roman legions
• Legionary
• Cohort
• Century
• Contubernium
• Centurion
• Legate

II. Units and services

• Auxilia
• Praetorians
• Ancient Roman navy
• Castrum

III. Equipment

• Roman army helmets
• Scutum
• Gladius
• Pilum
• Lorica segmentata
• Lorica hamata
• Lorica squamata

Literature

Ancient sources

1. Polybius. The Histories. 2. Julius Caesar. Commentaries on the Gallic War. 3. Vegetius. Epitoma Rei Militaris.

Modern studies

1. Adrian Goldsworthy. The Complete Roman Army. 2. Lawrence Keppie. The Making of the Roman Army. 3. M. C. Bishop, J. C. N. Coulston. Roman Military Equipment. 4. Yann Le Bohec. The Imperial Roman Army.

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