ORB Online Encyclopedia
Late Antiquity in the Mediterranean
The Late Roman Army
The birth of the Late Roman Army is usually taken to be the reforms of Diocletian (284-305) and Constantine (305-337). Their reforms were not completely innovative and forerunners of all their changes can be seen in the institutions and practices of the army of the third century AD. From the early fourth century, the army was a remarkably stable institution with few changes in practice or structure, suggesting that contemporaries were satisfied with its effectiveness.
The major development from the army of the principate was the formal division of the army into two parts, the field army (comitatenses) and the border troops (limitanei). The border troops were organized to defend provinces and were stationed around the edges of the Empire. In the mid-fourth century there were three regional armies (Gaul, Illyricum, the East), each commanded by a magister militum, and a praesental army attached to each emperor. In the late fourth century a series of smaller local field armies was created (e.g. in Britain, Africa and Thrace). These field armies moved to deal with crises as they occurred. The entire establishment was c. 450,000 men, but each field army could deploy 30-40,000 men. For offensives, praesental armies sometimes reinforced regional armies.
In both field and border forces the maneuver units were the same. Roman officers (tribunes, praepositi or praefecti) commanded legions (1200 men), cavalry regiments (600), or auxiliary infantry regiments (600). Most infantry were equipped with body armor, shield and spear, though regiments of archers and slingers also existed. Cavalry regiments ranged from light cavalry armed with bows or javelins to cataphracts, armored men on armored horses, equipped with lance and shield for charging into contact. The emperors' guards, the Scholae Palatinae, were all cavalry regiments. Naval units, engineers, medical services, intelligence services and a full logistical service supported the land combat troops.
Infantry dominated the army numerically and these formed the basis of tactics throughout this period. Cavalry deployed on the wings in support of the infantry (and it was the failure of the Roman left flank cavalry to cover the infantry at Adrianople in 378 that led to the loss of the battle). From the late fifth century, cavalry became more important on the battlefield, but infantry still made up the bulk of Roman armies.
Many fortifications lined the borders of the empire, garrisoned by troops of the border forces (which included naval units). Many cities within the Empire also had defenses. These fortifications had crenelated walls (c. 10 meters high, 2-3 m. thick), defensive ditches and protruding towers. Some also had artillery (bolt-shooters and stone-throwers) to supplement the garrison.
Individual soldiers served for twenty to twenty-five years and received a discharge bonus. Many of these recruits came from military families and many came from beyond the empire, a process misleadingly described as barbarization.
From the late fourth century onwards, the Romans made increasing short-term use of contingents of barbarian allies, a second process also known as barbarization. These were used to supplement Roman forces, but also as a military necessity. To take a Roman army away from an area containing recently settled barbarians was to invite disaster, especially in a civil war, where one's opponent would encourage them to revolt.
But why were such barbarian groups in the Empire in the first place? The direct cause was not the loss of the battle of Adrianople in 378, but the failure after this to destroy the Goths who were in the Empire. After their settlement in 382, the external threats did not diminish, but the Goths created an additional internal threat. The second major problem was the loss of Africa to the Vandals, which reduced the financial basis of the western empire. Without money to pay for troops, the military capacity of the west decreased, though the eastern empire remained intact. Loss of territory and financial crises, not a failure in military effectiveness, led to the collapse of the Roman West.
Cameron, A., The Later Roman Empire (Cambridge, MA, 1993), chapter 9
A Short Bibliography
Elton, H.W., Warfare in the Roman World (Oxford, 1996)
Jones, A.H.M., Later Roman Empire (Oxford, 1964), chapter 17
Liebeschuetz, J.H.W.G., Barbarians and Bishops (Oxford, 1991)
"Barbarization" in the Late Roman Army
Hugh Elton's Warfare in the Roman World Page
Late Antiquity Index