Roman to Byzantine Army Transition Part I

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Creation of the Medieval Roman Army

In 330 ce, Constantine I, Emperor of the Romans, founded a new capital for his empire on the triangular peninsula of land that divided the Bosphorus from the Sea of Marmara, commanding the narrow water passage from the Black Sea to the Mediterranean. He named it Constantinople, and in time it grew to be not only one of the greatest cities of antiquity, but the center of one of the most impressive civilizations the world has ever seen: the Byzantine Empire.

Within 200 years, the Byzantines (or Eastern Roman Empire, as they styled themselves) had grown to massive proportions, controlling all of Italy, the Balkans, Greece, Asia Minor, Syria, Egypt, North Africa, and Southern Spain. Such an empire could be held together only by a strong and efficient military, and for several centuries the Byzantine army had no equal anywhere in the world.

Although the empire had expanded enormously through conquest, the basic role of the Byzantine army was defensive. Fortifying the long borders was out of the question, and since raiders and invaders could strike anywhere along the empire’s frontier, the army needed to be able to move quickly to meet these threats. Like their predecessors, the Roman legions, the Byzantine units formed a professional standing army which was trained to near-perfection as a fighting machine. Unlike the legions, however, the core of the army was cavalry and fast-moving foot archers. Speed and firepower had become the trademarks of the “new Romans.”

The stirrup reached the empire from China early in the fifth century, and increased the effectiveness of the cavalry enormously. Therefore, the core of the Byzantine army became the heavy cavalry. A typical heavy cavalryman was armed with a long lance, a short bow, a small axe, broadsword, a dagger, and a small shield. He wore a steel helmet, a plate mail corselet that reached from neck to thigh, leather gauntlets, and high boots. His horse’s head and breast might be protected with light armor as well. By the later empire, armor for both rider and horse became almost complete, especially in the frontline units. In a secondary role, unarmored light cavalry horse archers on smaller mounts supported the heavy units with missile fire, while other light cavalry armed with a long lance and large shield protected their flanks.

The infantryman who usually accompanied the cavalry in the field was either a lightly armored archer who used a powerful long bow, a small shield, and a light axe, or an unarmored skirmisher armed with javelins and shield. Because most Byzantine operations depended on speed, tactically as well as strategically, heavy infantry seldom ventured beyond the camps or fortifications. The heavy infantryman wore a long mail coat and steel helmet and carried a large, round shield. He used a long spear and a short sword. The Varangian Guard, the emperor’s personal bodyguards, were famous for their great two handed axes which they wielded with great effect. Their armor was almost complete plate and mail from head to foot.

To the Byzantines, war was a science, and brains were prized over daring or strength. Military manuals such as the Strategikon (ca. 580) and the Tactica (ca. 900) laid down the basics of military strategy that really did not vary for almost a thousand years. The army was always small in number (field armies almost never exceeded 20,000 men, and the total force of the empire probably was never greater than 100,000) and, because of its training and equipment, very expensive to maintain. Huge losses in combat could be catastrophic, and seldom were great winner take-all battles fought. The goal of any Byzantine general was to win with the least cost. If by delay, skirmishing, or with drawing the local population and their goods into forts he could wear out an invading force and cause it to withdraw without a costly pitched battle, so much the better. Bribing an enemy to go away was also quite acceptable.



Like all armies, ancient and modern, the Byzantines arranged their military apparatus hierarchically. The handbooks portray deep organizational structures, inherited from the Romans and persisting until the fall of the empire, with clearly delineated ranks to the level of five or four soldiers. The overall commander of the army was, of course, the emperor. In all cases emperors were expected to uphold the façade of military competence—even the most pacific possessed a smattering of training, could ride, wield weapons, and were literate in strategy and the structure of their forces. In many instances, the emperors were military men and possessed firsthand experience in the affairs of war. Since no head of state could manage security alone, even when he took the field himself, all relied heavily on practiced commanders.

Constantine appears to have made radical structural changes in military organization; he removed the prefects from command and made theirs an administrative post. He further removed the troops stationed in garrison, the frontier guards (limitanei or ripenses), from the emperor’s guard units (protectores) and the field army (comitatenses), which he expanded in size. Units were uprooted and pulled from their old third-century bases. The Master of Infantry (magister peditum) and Master of Cavalry (magister equitum) commanded those branches of individual field armies. We would equate the various magistri with marshals in more modern military parlance, with control over armies in a given theater. After Constantine the empire was once more divided between emperors in east and west and some mobile units transferred to the frontiers where they formed the core of campaign armies and an effective active defense supplemented by the limitanei. Such mobile regional field forces were under the command of a Master of Cavalry who commanded both the infantry and horse.

Prior to Constantine, Diocletian replaced the old Praetorian Guard—which had become infamous through fractiousness, rank insubordination, and regicide—with a new imperial bodyguard. Constantine further increased the new regiments, the Scholae (Latin: schools, group), which totaled twelve units, each with 500 men divided evenly between eastern and western halves of the empire. The magister officiorum (Master of Offices) led them. These units formed an elite guard for the emperor on campaign through the time of Theodosius I (379–95), but most units gradually declined to a civilian honor guard by the later fifth century. By the sixth century a count (comes domesticorum) commanded units of the scholae.

In the fifth century, the strategic disposal of forces and consequently the high command settled into the form it would resemble through the reign of Justinian. There were two imperial armies attached to the emperor’s person led by the magister militum praesentalis (Master of Soldiers of the Emperor’s Presence). These praesental armies comprised elite troops and mobile field forces that would form the core of any imperial expeditionary force. Five regional field armies (two praesental armies, Illyricum, Thrace, and the East) and their supporting frontier forces were under the command of the magister utriusque militiae (Master of Combined Forces [meaning of horse and foot]). His lieutenant, the vicarius, is known from the fifth century onward. There were frontier commands directed from the office of comes rei militaris (military counts) in Egypt and Isauria in mountainous and restive southern Asia Minor and thirteen dukes along the Danube, eastern frontier, and Libya. The magister commanded his field forces and also held authority over the armies under control of the comites and duces. The legatus (legate) or prefects held the reins of individual infantry legions. Infantry cohorts (regiments) of 500–600 still existed in the fourth century and their cavalry equivalent was formed of vexillations (vexillatio) or alae of up to 500 troopers. Tribune was the most common title for officers handling regiment-sized units, whether cavalry or infantry, but we also find the prefect in command of the cavalry vexilliations, alae, and among the limitanei. Another vicarius (hence our word “vicar”) was the lieutenant commander of the regiment whose duties and authority increased throughout this period. While much of the army underwent serious changes in organization and deployment, certain areas, such as Egypt, retained older structures and ranks.

Promotion within the ranks was a matter of service time or, not uncommonly, graft. St. Jerome (d. 420) provides a clear hierarchy of grades for enlisted men and noncommissioned officers in the early Byzantine period. He lists from lowest to highest grade: tiro; eques/pedes; circitor; biarchus; centenarius; ducenarius; senator; and primicerius.

A recruit was a tiro (pl. tirones) until he was trained, and such men did not draw full pay or rations. The anonymous author of a late fourth-century document, the De Rebus Bellicis (Military Affairs), recommended that cohorts maintain fifty or a hundred tirones so that losses could be quickly and cheaply replaced. Soldiers of the line were pedes (infantry) or eques (cavalryman). The semissalis seems to have been a senior ranker but below what we would consider noncommissioned officer status. At the base of the noncommissioned officer ladder of that time, the circitor at one time inspected sentries but little else is known of his authority or responsibilities. By the fourth century he may have been a junior biarchus, (mess-leader; sometimes called decanus or dekarch, “leader of ten,” even though he led eight soldiers, including himself) who commanded the contubernium, the squad or mess-group, which comprised eight to ten men who shared a tent and, as the name suggests, took meals together. By the fourth and fifth centuries the century numbered around eighty men, ten contubernia, commanded by the centurion with the rank of centenarius. The ducenarius, rather than commanding two centuries, was probably a higher-ranking centurion, since Vegetius stated that these men formerly commanded two hundred, an indicator that the title no longer reflected its old order. As historian Warren Treadgold argues, the senator likewise was probably a senior kind of noncommissioned officer with specialist duties, such as adjutor (clerk or scribal assistant), campidoctor (a centurion who drilled rankers and recruits), or actuarius (regimental quartermaster). Each regiment also had an optio (quartermaster), a surgeon, two heralds, two standard bearers, draconarii—named for the dragon-headed pennons known in the fourth century, a cape bearer, a trumpeter, and a drummer.

The five regional field armies possessed an extensive administration that handled correspondence, pay, logistics, and judicial matters. These large staffs, numbering up to three hundred, mirrored their civilian counterparts in the provinces. Military tribunals were more or less the same throughout the staffs of the magister militum, the dux, or the comes. The army judiciary was staffed by a princeps assisted by a commentariensis and an adiutor and a libellis; the latter dealt with judicial petitions. Deputy assistants (subadiuva) and shorthand writers (exceptores) handled the judicial clerking. Another bureau headed by a princeps with his assistant, the primiscrinius, two numerarii (principal accountants), and their support staff of scriniarii (clerks) dealt with financial and supply matters.

Scholars debate the tenor and role of the frontier forces (limitanei) who are sometimes characterized as “static” forces or even as “soldier-farmers” whose quality deteriorated in the fifth and sixth centuries. In a much-cited passage written no later than the year 550, Prokopios criticized Justinian for his elimination of their pay. While the loss of payment in coin may be true, frontier garrisons staffed by local troops continued to exist in some areas of the empire. An Egyptian known as Flavius Patermuthis (the name “Flavius” was taken upon entry into imperial service from the reign of Constantine to show one’s joining the imperial “family”) served as a soldier in Elephantine (modern Aswan, Egypt) from at least 585–613. Patermuthis and his comrades were prominent locals, indicating that in some places the limitanei had come to resemble local self-help forces rather than disciplined professionals. Elsewhere, the picture is somewhat different. Isaac argues that the limitanei were not soldier-farmers but simply the troops under the command of the duces of the provinces and as such they were mobilized for police duties and patrols, manned the frontier posts, and joined the field army on campaign. From papyri recovered in Nessana (modern Nitzana in southern Israel) we know of a numerus of dromedarii (camel riders) who patroled the desert routes around Gaza; these men appear as landowners and prominent members of the community until around 590, when the unit was either disbanded or transferred. Their duties were then probably assumed by allied Arab forces of the great confederation of Ghassan.

Federate soldiers (foederati) remained prominent in the Roman military structures of the fourth to seventh centuries. These troops served under a treaty (foedus) between the empire and tribes on the frontier. During the time of Diocletian and Constantine, federate troops served under their own commanders and were paid lump sums with which to provide for their soldiers’ needs. They also received annona: payment in kind of foodstuffs and fodder. By the sixth century, some tribal groups served under their own leaders in this fashion, such as the Ghassanid Arabs who guarded the eastern frontier from the Euphrates to the Red Sea. Others federates were enrolled in regular military units that appear to have been mixed Roman-barbarian contingents under the command of Roman officers. When not in the field these units were under the authority of the comes foederatorum, but for tactical purposes while on campaign they served under the magistri.

In 528, in light of new strategic realities in which the contest with Persia increasingly centered on Armenia and the Caucasus, Justinian divided the eastern command formerly under the magister militum per Orientem. He created a new command, the magister militum per Armeniam, headquartered at Theodosiopolis (modern Erzurum) whose army was drawn from both praesental units and the mobile forces of the old duces and comites of the frontier districts. Following their successful conquests, Africa, Italy, and Spain gained their own regional commands as well, which raised the number of army corps to nine, though there does not seem to have been a commensurate increase in troop numbers.

By the time of Maurice’s Strategikon in the late sixth or early seventh century, the army had changed considerably. The old guard units, the Scholae, Domestici, Protectores, and Candidati (originally a picked unit of the Scholae) became mostly civilianized but remained intact. The limitanei degraded and Justinian seems to have drawn down some of these frontier forces. The military returned to a purely decimal system of organization, with the main building blocks being the commands of ten and one hundred. A change in terminology reflects the decline of Latin in favor of Greek within the military, which was natural since the latter was the language spoken by most people in the eastern Mediterranean.

Book 1 of the Strategikon lays out the ideal officer structure of the Maurician army at the end of the sixth century. The general, now called by the Greek title strategos, held overall command of a given field army. A hypostrategos (lieutenant general) served as his second in command and led the meros (division) in the center of the battle line; this indicates that tactically the hypostrategos was important, since his forces anchored the army. The handbook also says that armies of medium strength were 5,000–12,000, thus representing groups of one to three meroi. A meros (Greek “part,”“portion”) was a division comprised of around 5,000 men, officered by a merarch. The division meros was built from multiple units called moira. The moira numbered 2,000–3,000 under the command of a duke, moirarch, or chiliarch. The units that replaced the cohorts of the older army were variously called tagma (not to be confused with the imperial mobile army which had taken on the name tagma or tagmata after the Greek for “order” or “ranks”), arithmos, or bandon. The tagma and its equivalents numbered 200–400 led by a count or tribune, with his second in command, the ilarch, a higher grade hekacontarch who commanded a hundred men. The hekacontarch then was the successor to the old legionary centurion. The lowest levels of command were the dekarch, pentarch, and tetrarch who commanded ten, five, and four men, respectively (including themselves).

The Strategikon provides the order of march for a 310–man cavalry tagma, probably a common strength (for a number of reasons, unit sizes were not uniform). The commanding officer (tribune or count) held under his command two hekacontarchs (or ilarchs), 27 dekarchs, 29 pentarchs, 31 tetrarchs, a standard bearer, a cape bearer, and a trumpeter, with 217 troopers. Treadgold hypothesizes that the tactical units mentioned in the text, ranging from 200–400, represent deployments from standard, 500 men regiments (tagma or bandon) whose remaining 100–300 men remained in quarters. This is a reasonable interpretation, given that unit sizes seem to have been based on decimal units grouped into thousand-man paper legions whose disposition varied according to the tactical situation.

The Strategikon names among mobile field meroi, the Optimates (“best men”), an elite cavalry regiment (bandon) unit of perhaps 1,000 men. In addition, elite cavalry units clearly owed their names to older Roman forces: the Vexillations, Illyriciani, and Federates, all mobile cavalry divisions that Treadgold estimates numbered around 5,000 each. Haldon sees there being only three elite cavalry units: the Optimates, Boukellarii, and Federates, all formed sometime after 575. These cavalry armies probably replaced the old praesental armies as the core of imperial campaign forces, since the author of the Strategikon envisions deployment of the three in the vanguard of an imperial campaign army.

The Persian War of Heraclius occupied more than a decade and drained the empire of men and resources. By the mid-620s the Romans had rebuilt their forces and attained victory, only to see them swept away by the armies of Islam. The Byzantines adapted to these exigencies by reconstituting their battered forces as best they could and billeting troops throughout the countryside of Asia Minor, the last large territory left in imperial possession. From the settlement of the military corps on the land evolved a new military and administrative apparatus called the theme system. Thema (theme) is a word of unknown origin, but may be derived from the army muster rolls or the tax rolls needed to support them. During the Persian campaigns of Heraclius the term simply meant headquarters of an army command. The earliest attested themes seem to date to the mid-or late seventh century. “Theme” as a territorial and army designator probably derived from the association in the minds of administrators with the cataloging of military men and corresponding territory and material needed to sustain them.


How did the Byzantine army evolve from the Roman army?

The Byzantine army was a direct continuation of the Eastern Roman army. It maintained a similar level of discipline, strategy, and organization, but over time adapted to new military tactics and influences from Germanic and Asian cultures.

What were the major changes in the Byzantine military system?

One significant change was the shift from the traditional Roman legion system to the thematic system during the 7th century, where land was granted to farmers who, in return, provided military service. This system allowed the Byzantine army to increase their defensive stance against threats while securing loyalty.

What role did mercenaries play in the Byzantine army?

Mercenaries became increasingly important in the Byzantine army when the thematic system collapsed. Byzantine emperors relied on foreign mercenaries to supplement their forces due to the diminished local recruitment after the loss of Asia Minor​.

Forschungsmitarbeiter Mitch Williamson is a technical writer with an interest in military and naval affairs. He has published articles in Cross & Cockade International and Wartime magazines. He was research associate for the Bio-history Cross in the Sky, a book about Charles ‘Moth’ Eaton’s career, in collaboration with the flier’s son, Dr Charles S. Eaton. He also assisted in picture research for John Burton’s Fortnight of Infamy. Mitch is now publishing on the WWW various specialist websites combined with custom website design work. He enjoys working and supporting his local C3 Church. “Curate and Compile“
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