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Imperial Roman army

The Imperial Roman army was the military land force of the Roman Empire from 27 BC to 476 AD,[1] and the final incarnation in the long history of the Roman army. This period is sometimes split into the Principate (27 BC – 284 AD) and the Dominate (284–476) periods.

Roman army

27 BC to 476 AD

450,000 (211 AD)

Emperor (de facto)
Consuls (de jure)

Under Augustus (r. 27 BC – AD 14), the army consisted of legions, eventually auxilia and also numeri.[2] By the end of Augustus' reign, the imperial army numbered some 250,000 men, equally split between 25 legions and 250 units of auxiliaries. The numbers grew to a peak of about 450,000 by 211, in 33 legions and about 400 auxiliary units. By then, auxiliaries outnumbered legionaries substantially. From this peak, numbers probably underwent a steep decline by 270 due to plague and losses during multiple major invasions by the Germanic Tribal Folk. Numbers were restored to their early 2nd-century level of c. 400,000 (but probably not to their 211 peak) under Diocletian (r. 284–305).


After the Empire's borders became settled (on the Rhine-Danube line in Europe) by AD 68, virtually all military units (except the Praetorian Guard) were stationed on or near the borders, in roughly 17 of the 42 provinces of the empire in the reign of Hadrian (r. 117–138).

History[edit]

Background[edit]

The army of the late Republic that Augustus took over on becoming sole ruler of the Empire in 27 BC consisted of a number of large (5,000-strong) formations called legions, which were composed exclusively of heavy infantry. The legion's light infantry (velites) which had been deployed in earlier times (see Roman army of the mid-Republic), had been phased out as had its contingent of cavalry. Legions were recruited from Roman citizens only (i.e., from Italians and inhabitants of Roman colonies outside Italy), by regular conscription, although by 88 BC, a substantial proportion of recruits were volunteers.


To remedy the deficiencies in capability of the legions (heavy and light cavalry, light infantry, archers and other specialists), the Romans relied on a motley array of irregular units of allied troops, both composed of subject natives of the empire's provinces (called the peregrini by the Romans) and of bands supplied, often on a mercenary basis, by Rome's allied kings beyond the Empire's borders. Led by their own aristocrats and equipped in their own traditional fashion, these native units varied widely in size, quality and reliability. Most would only be available for particular campaigns before returning home or disbanding.

Denarius minted by Mark Antony to pay his legions. On the reverse, the aquila of his Third legion.

Denarius minted by Mark Antony to pay his legions. On the reverse, the aquila of his Third legion.

Antoninianus minted under Carausius. On the reverse, the lion, symbol of the Legio IV Flavia Felix, and the legend LEG IIII FL.

Antoninianus minted under Carausius. On the reverse, the lion, symbol of the Legio IV Flavia Felix, and the legend LEG IIII FL.

Sestertius minted in 248 by Philip the Arab to celebrate the province of Dacia and its legions, V Macedonica and XIII Gemina. Note the eagle symbol on the reverse of legio V [left]

Sestertius minted in 248 by Philip the Arab to celebrate the province of Dacia and its legions, V Macedonica and XIII Gemina. Note the eagle symbol on the reverse of legio V [left]

Gallienus coin, celebrating LEG VII CLA VI P VI F (Seventh legion Claudia, six times faithful, six times loyal), and bearing the bull, symbol of the Legio VII Claudia, on the reverse.

Gallienus coin, celebrating LEG VII CLA VI P VI F (Seventh legion Claudia, six times faithful, six times loyal), and bearing the bull, symbol of the Legio VII Claudia, on the reverse.

Memorial to Lucius Duccius Rufinus, a standard bearer of the Legio IX Hispana, Yorkshire Museum, York

Memorial to Lucius Duccius Rufinus, a standard bearer of the Legio IX Hispana, Yorkshire Museum, York

Sestertius minted in 248 by Philip the Arab to celebrate the province of Dacia and its legions, V Macedonica and XIII Gemina. Note the lion, symbol on the reverse of the legio XIII (right).

Sestertius minted in 248 by Philip the Arab to celebrate the province of Dacia and its legions, V Macedonica and XIII Gemina. Note the lion, symbol on the reverse of the legio XIII (right).

Aureus minted in 193 by Septimius Severus, to celebrate XIIII Gemina Martia Victrix, the legion that proclaimed him emperor. Legion emblem was the Capricorn.

Aureus minted in 193 by Septimius Severus, to celebrate XIIII Gemina Martia Victrix, the legion that proclaimed him emperor. Legion emblem was the Capricorn.

Emblem of the 20th Legion Roof Tile

Emblem of the 20th Legion Roof Tile

Roman army

Auxilia

Campaign history of the Roman military

Equestrian order

Structural history of the Roman military

Auxiliaries in Britain (Roman military)

List of Roman auxiliary regiments

List of Roman legions

Veteran (Roman history)

Acies contra Alanos (c. AD 140)

Arrian

De Bello Gallico (c. 50 BC)

Caesar

Roman History (c. AD 240)

Dio Cassius

Ab urbe condita (c. AD 20)

Livy

De Vita Caesarum (c. AD 120)

Suetonius

Agricola (c. AD 100)

Tacitus

Annales (c. AD 100)

Tacitus

Historiae (c. AD 100)

Tacitus

De Re Militari (c. AD 390)

Vegetius

Roman Legionary AD 69-161

Roman Guardsman 62 BC - AD 324

Roman Military Diplomas Online

Batavian auxiliaries re-enactors

List of auxiliary units in Britain

Vindolanda Tablets Online