The Eastern Roman army refers to the army of the eastern section of the Roman Empire, from the empire's definitive split in 395 AD to the army's reorganization by themes after the permanent loss of Syria, Palestine and Egypt to the Arabs in the 7th century during the Byzantine-Arab Wars. The East Roman army was the continuation of the Late Roman army of the 4th century, until it gradually transformed into what is now called the Byzantine army from the 7th century onwards.
The East Roman army was a direct continuation of the eastern portion of the late Roman army as it existed before the final division of the empire. The East Roman army initially maintained the same basic organization as the late Roman army and its West Roman counterpart, but gradually underwent significant structural changes between the 5th and 7th centuries. Cavalry became more important, mobile field armies took on a more prominent role, and the border armies were eventually transformed into local militias.
In the 6th century, Emperor Justinian I, (), sent much of the East Roman military to participate in the partial reconquest of several portions of the former Western Roman Empire. In these wars, the Eastern Roman Empire reconquered parts of North Africa from the Vandal Kingdom, most of Italy from the Ostrogothic Kingdom, and parts of southern Spain. The strength of the East Roman army diminished greatly during Justinian's reign, due in large part to the severe demographic impact of the Plague of Justinian on the population of the Eastern empire. In the 7th century, the East Roman army fought a long and destructive war against the Sasanian Empire under the leadership of Heraclius. Heraclius temporarily regained Egypt and Syria from the Sasanians, but almost immediately faced an invasion by the expanding Rashidun Caliphate. His generals’ defeat at the Battle of Yarmuk lead directly to the Islamic conquest of Syria and Egypt, and ultimately caused the reorganization of the East Roman army into the thematic system of later Byzantine armies.
Sources
Much of the evidence for the East Roman army's deployments at the end of the 4th century is contained in a single document, the Notitia Dignitatum, compiled c. 395–420, a manual of all late Roman public offices, military and civil. The primary deficiency of the Notitia as a source is its lack of any personnel figures, making estimates of army size difficult or impossible. Despite this, the Notitia remains the central source on the late Army's structure due to the dearth of other evidence.
The Strategikon of the Emperor Maurikios, from the end of the 6th century, describes the cavalry tactics, organization, and equipment of the East Roman army towards the end of this period.Elton, Hugh, "Army and Battle in the Age of Justinian," in Erdkamp, Paul, A Companion to the Roman Army, p. 533. The De re militari of Vegetius, probably from the beginning of the 5th century, calls for reform of the West Roman army, which was similar to the East Roman army. However, the De re militari emphasizes the revival of earlier Roman practices, and does not provide a clear view of the tactics, organization, and practices of any branch of the late Roman army.
The histories of Ammianus Marcellinus provide a glimpse of the late Roman army before the division of the Roman Empire. Those of Procopius, especially his Wars and parts of his Buildings, written while accompanying the magister militum Belisarius during the emperor Justinian's wars against the Sassanid Empire and the barbarian successor kingdoms, provide a view of the East Roman army in the period, and its campaigns. The histories of Agathias and Menander continue those of Procopius.
Another major source for the East Roman army includes the legal codes published in the Eastern Roman Empire in the 5th and 6th centuries: the Theodosian code (438) and the Corpus Iuris Civilis (528-39). These compilations of Roman laws dating from the 4th century contain numerous imperial decrees relating to the regulation and administration of the late army.
Origins and history
In 395, the death of the last sole Roman emperor, Theodosius I (), led to the final split of the empire into two political entities, the West (Occidentale) and the East (Orientale). A system of dual emperors (called Augusti after the founder of the empire, Augustus), each ruling one half of the empire as nominal imperial partners, had been instituted a century earlier by the reforms of the emperor Diocletian (). This had never been envisaged as a true political separation, but rather as an administrative and military necessity. Decrees issued by either emperor were valid in both halves of the empire, and the successor of each Augustus required the recognition of the other. The empire was reunited under one emperor under Constantine I after 324, under Constantius II after 353, under Julian after 361, and under Theodosius himself after 394.
The division of the Roman state into two sections accompanied a growing cultural divergence between east and west. The common language of the East had always been Greek, while that of the West was Latin. This was not per se a significant division, as the empire had long been a fusion of Greek and Roman cultures (classical civilisation) and the Roman ruling class was entirely bilingual. But the rise of Christianity strained that unity, as the religion was always much more widespread in the East than in the West, which was still largely pagan in 395. Constantine's massive reconstruction of the city of Byzantium into Constantinople, a second capital to rival Rome, led to the establishment of a separate eastern court, senate and administrative bureaucracy.
The political split became institutionally formalized over the course of the collapse of the Western Roman Empire in the 5th century, during which the central authority of the Western emperor was gradually supplanted by the local rule of a number of barbarian Germanic chieftains. Following the deposition of Western emperor Romulus Augustulus by Ostrogothic leader Odoacer in 476, the senate in Rome sent the Western imperial insignia to Constantinople, along with a message recognizing Eastern emperor Zeno as sole Augustus. In response, and in tacit acceptance of the new political order, Zeno declined to nominate an imperial colleague in the West, breaking with the dual-emperor system enacted by Diocletian more than 150 years prior. Zeno instead recognized Odoacer as a nominally-subordinate imperial viceroy in Italy, although in practice, both Odoacer and his Germanic contemporaries ruling other areas of the former Western empire were independent from Roman rule.
By this time, the Western Roman army consisted primarily of foederati, non-Roman barbarian troops operating under the command of their own chieftains, functionally independent from the Western imperial court in Ravenna. As these chieftains asserted their independence from imperial authority, simultaneously removing their troops from imperial command, the Western Roman army also therefore ceased to exist as an institution.
The Eastern Roman army, on the other hand, maintained a structure that was administratively continuous with the Late Roman military of the 4th century AD, undergoing gradual changes until experiencing radical reform in the wake of the Persian and Arab invasions of the 7th century. On the eve of these invasions, at the end of the 6th century, the East Roman army still adhered to the same basic division between mobile field armies (comitatenses) and frontier troops (limitanei) that existed in the 4th century. Despite this high-level structural continuity, throughout the 5th and 6th centuries, several important changes took place, including an erosion of previously strict organizational boundaries between Roman troops and non-Roman foederati allies, as well as an increasing reliance on bucellarii, the household guard units of high-ranking Eastern Roman officers and officials.
Following Eastern empire's loss of its dominions in the Near East and North Africa, especially Egypt, to the Arab invasions of the 7th century, the East Roman military underwent a dramatic structural re-organization into the theme system. Mobile field armies were settled in military-administrative districts within the empire's remaining territories in Asia Minor, Greece and the Balkan peninsula, eliminating the longstanding distinction between the field armies and frontier troops. This is generally understood as the transition point between the East Roman army of Late Antiquity, and the Byzantine army of the early medieval period.
Army size Warren Treadgold estimates that the Eastern Roman army had about 3,500 scolae or guards, 104,000 field army soldiers, with an uncertain number of sailors, and 195,500 border army soldiers, again with an uncertain number of sailors, in 395.Warren Treadgold, Byzantium and its Army, 281-1081, pp. 44-59.
Treadgold also estimates that the Eastern Roman army had about 150,000 field army soldiers, in 559, late in the period of Justinian.Warren Treadgold, Byzantium and its Army, 281-1081, pp. 59-64. He later estimated that the number of frontier troops and sailors was 229,000, which brought the total size of the army to well over 300,000.Treadgold, Byzantium And Its Army, 1995, pp. 161-162
Treadgold also estimates that the Eastern Roman army had about 80,000 field army soldiers, with an uncertain number of sailors, in 641, after the Islamic conquest of Syria and Egypt.Warren Treadgold, Byzantium and its Army, 281-1081, p. 64.
Numbers
The size of the Eastern army in 395 is controversial because the size of individual regiments is not known with any certainty. Plausible estimates of the size of the whole 4th-century army (excluding fleets) range from c. 400,000Elton (1996) 120 to c. 600,000.Jones (1964) 683 This would place the Eastern army in the rough range 200,000 to 300,000, since the army of each division of the empire was roughly equal.Heather (2005) 247
The higher end of the range is provided by the late 6th-century military historian Agathias, who gives a global total of 645,000 effectives for the army "in the old days", presumed to mean when the empire was united.Agathias History V.13.7-8; Jones (1964) 680 This figure probably includes fleets, giving a total of c. 600,000 for the army alone. Agathias is supported by A.H.M. Jones' Later Roman Empire (1964), which contains the fundamental study of the late Roman army. Jones calculated a similar total of 600,000 (exc. fleets) by applying his own estimates of unit strength to the units listed in the Notitia Dignitatum. Following Jones, Treadgold suggests 300,000 for the East in 395.Treadgold (1995) 45
But there are strong reasons to view 200,000 as more likely:
Jones' assumptions about unit strengths, based on papyri evidence from Egypt, are probably too high. A rigorous reassessment of the evidence by R. Duncan-Jones concluded that Jones had overestimated unit sizes by 2-5 times.Duncan-Jones (1990) 105-17 The evidence is that regiments were typically one-third understrength in the 4th century.Elton (1996) Thus Agathias' 600,000 on paper (if it is based on official figures at all) may in reality have translated into only 400,000 actual troops on the ground. Agathias gives a figure of 150,000 for the army in his own time (late 6th century) which is more likely to be accurate than his figures for the 4th century. If Agathias' 4th- and 6th-century figures are taken together, they would imply that Justinian's empire was defended by only half the troops that supposedly defended the earlier empire, despite having to cover even more territory (the reconquered provinces of Italy, Africa and S. Spain), which seems inherently unlikely.