Civil And Military Organization Of The Later Roman Empire



Current news headlines of populations on the move into Europe have drawn attention to a previous era in European history, one in which mass migrations of foreign peoples played a major role.  The Roman Empire of the fourth and fifth centuries was faced with these very challenges from the movements of Germanic tribes, as well as Avars, Bulgars, and Huns.

As I looked more into the details of this period of history, I was struck with how resilient and stable the Empire’s organization was.  There is vast ignorance of this period of history, even (or especially) among Europeans.  While it is often portrayed as an age of continuous decline and decadence, this picture is not the whole truth.

The civil and military organization established by Constantine was wise and enduring, and it deserves to be better known.  It stands in stark contrast to the ineptitude and feebleness of the heads of state in modern Europe.

This article is technical in nature, and will be of interest to the few, rather than to the majority.  Those comprising the latter group may wish to pass on this post, and spare themselves some heaviness of the eyelids.

Diocletian And Constantine

Diocletian (A.D. 245-311) had inherited an empire that had become far too vast a domain for one man to govern effectively.  The territories of Rome extended from Britain and Spain in the West, nearly all of Europe except Germany and Sarmatia (the lands north of the Balkans), across the entirety of North Africa, Asia Minor, and the area of the Fertile Crescent (Syria) up to the border of an ancient enemy, Persia.

All of these lands were inhabited by diverse peoples, each with their own languages, customs, and municipal institutions.  Within this immense area, two distinct cultural spheres had emerged:  the Latin-speaking West, and the Hellenized East.  The Latin language took root firmly in the West, but Greek always remained the language of the educated elites in the East; the common populations there were too ancient, and too subtle, to surrender their linguistic traditions to the Caesars.

Thus Coptic stood its ground in Egypt, Syriac and Aramaic in Syria, and Armenian in Armenia.  But although the empire had distinctly western and eastern halves, the sovereigns and citizens of the time always saw the empire as one entity.

One of Diocletian’s major achievements was to reorganize the empire into effective administrative units.  His reign as emperor (284-305) saw the most profound changes to the structure of the empire since its founding.  He divided Rome’s holdings into ninety-six provinces; these were additionally categorized by dioceses and prefectures.  The empire that had been founded by Augustus three centuries earlier was very different from the one ruled over by Diocletian, and he rightly believed that political institutions needed to keep pace with those changes.

Centuries of war (both external and civil), economic conditions, population movements, and the rise of a new religion (Christianity) had changed the landscape thoroughly. Augustus had chosen to retain the fig-leaf of republican institutions to his empire.  In theory, the responsibilities of power were shared between the emperor (princeps) and the Roman Senate.

In practice, of course, the emperors had usually felt free to do as they liked without regard for what the Senate had to say.  But at least lip-service was paid to the old republican institutions and offices, such as the consul, praetor, aedile, censor, and the rest.

Diocletian swept away these outmoded republican pretensions and made Rome a frankly oriental autocracy.  The importance of these changes cannot be overstated.  From the end of the reign of Commodus in 192 to the accession of Diocletian, twenty-eight men had worn the imperial purple; and of these, we are told, no less than twenty-two were murdered.[1]  Diocletian’s reforms were meant to put an end to contests for imperial succession, and to provide a mechanism for orderly transfers of power.

His system was in theory a cooperative one:  an emperor would rule with the help of a co-emperor, and each emperor would in turn rely on a vice-emperor.

Diocletian in 286 appointed his close colleague Maximian to be his co-emperor; he and Diocletian would share the title of Augustus.  Maximian was an efficient and ruthless administrator, and absolutely loyal to his patron; these qualities made him an ideal candidate for the office.  In theory, both Augusti had equal power to issue decrees, but of course in practice it was Diocletian, as the senior man, who played the dominant role.

After nine years of this arrangement, both men chose colleagues of their own, who would be termed Caesar.  Each Caesar would be able to replace his Augustus if death or absence should remove the latter, thereby neatly solving the problem of succession that had so plagued the imperial throne for a century.  This system came to be called the “tetrarchy.”

The problem with the system was that it did not work.  Instead of one or two claimants to the throne battling for supremacy, there were now four potential dynasts, all at each other’s throats.  The co-regent system proved itself to be clumsy and incapable of meeting the challenges of succession.  When Diocletian and Maximian retired in 306, a new round of armed combat began for the privilege of wearing the imperial robe and diadem.

These struggles need not detain us long here; we need only note that by 308 there were four Augusti presenting themselves as rightful rulers.  When the dust of combat had settled, Constantine I (later called “The Great”) had himself declared sole Augustus in 324.  His method of resolving succession problems was to adopt the time-honored solution of heredity:  blood was to him more reliable than titles.

So in 324 he appointed his sons Constantine, Crispus, and Constantius as Caesars, and eleven years later added to this list Delmatius and Hannibalianus.  As is often the case with the progeny of a great man, these sons never succeeded in moving out of the shadow cast by their father; they were “Caesars” in name only.  To emphasize this point,   Constantine had one of his sons, Crispus, executed in 326.[2]

Constantine, among his many strokes of administrative genius, recognized that Rome could no longer serve as the effective capital of the empire’s vast holdings.  It had too much of what we would today call “baggage”; it was far from the real center of economic power (which was now in the East, and it was haunted by the ghosts of centuries of intrigue and conspiracy.  The site of ancient Byzantium was perfect for his purposes.

The city as he found it had been destroyed and then partially rebuilt by his predecessor Septimus Severus.  Constantine had his new capital constructed over a period of six years, and finally consecrated the new trapezium-shaped city of Constantinople in 330.  The city was known at the time as New Rome.

Constantine remained the sole ruler until his death in 337.  Then another round of conflict and bloodshed ensued, as rival family claimants battled with each other for the imperial prize.  Constantius, the sole surviving son of Constantine the Great, emerged as sole Augustus in 353 after the suicide of his main rival Magnentius.  To prevent any rival from contesting his rule in the future, Constantius preserved the careful balance of administrative powers in the empire.

He employed all the usual ruses that sovereigns have found expedient to retain their positions:  establishing parallel civil and military chains of authority, deliberately creating redundancy in offices and titles to prevent one person from aggregating too much power, and employing an extensive network of informants and court officials.[3]  Elaborate ceremonies and customs were created to keep the emperor remote from daily affairs of state, and thereby maintain the aura around him.

Honorific titles like nobilissimus, sanctissimus, and even divinus came to be used in connection with the emperor; these were words which would have provoked amusement or derision in the early years of the empire.  Romans of the old republic, such as Cicero, would have been horrified.  Thus, as often happens in states equipped with monarchic dynasties, institutions proved less influential that the bonds of kinship.

Thus the principate became the tetrarchy, and then changed back into autocracy.  The emperor now had the full right of direct legislation through edicts, without having to explain himself to the Senate.  In theory this right had belonged to the Senate, but in the decades after Diocletian the emperors had arrogated to themselves this privilege.

After Julian the Apostate’s time—beginning in the fifth century—there did come into existence two important checks on the power of the monarch.  One of these was the Patriarch of Constantinople, who had the power to crown the emperor, and the other was the right of the populace to depose an emperor in a form of legal revolution.[4]  Constantine the Great had founded a new Senate in Constantinople, which was made an imperial body by his son Constantius.

Its responsibilities were both municipal and imperial; perhaps this was the reason why there were two separate Senate houses in Constantinople.[5]  This eastern Senate was not precisely the equivalent of the original body in Rome; the offices of aedile, tribune, and quaestor were phased out, and the office of praetor concerned itself chiefly with sponsoring public entertainments.

Membership of the Senate was frankly limited by heredity: sons of senators formed the main body of candidates, but newcomers could be elevated to senatorial office by imperial decree.  It was possible after Constantine for a man of common birth to rise through the government ranks to become a senator, but this was not the rule.

To assist in the duties of governance, there gradually came into existence a number of administrative offices, which are discussed in detail in Appendix A.  Besides the Senate, the emperor also governed with the assistance of an imperial council called the Consistorium.  This body functioned in practice much like a cabinet of advisors, and was tasked with helping the monarch deliberate on policies and proposed decrees.  It also seems to have acted as a kind of “supreme court” before which cases could be tried.[6]

The provinces of the empire were reshuffled by Diocletian into a complex and overlapping system of dioceses and provincial governors.  The leaders of these units possessed civil, and not military, powers.  Praetorian prefects controlled the civil administration of both of them.  Gaul, Italy, Illyricum, and the East were the four main administrative prefectures of the empire; and each of these was headed by a Praetorian prefect.


The prefectures were subdivided into dioceses, and each diocese was headed by a governor called a vicarius.[7]  The Praetorian prefect had a wide variety of administrative, financial, and judicial tasks; he was a man who commanded great respect, and military figures approaching him had to display their deference.  The prefects of the East and of Italy were the highest imperial officials after the emperor himself; Illyricum and Gaul were below them in rank.

Rome and Constantinople were special cases; they had their own prefect, who was called the Prefect of the City.  The various other civil and administrative offices of the empire were large in number, but need not detain us here.


What we should conclude from this overview of the empire’s administration are the following things.  First, the system was reasonably effective in maintaining stability.  For all its faults, the highly bureaucratic machinery functioned well under pressure; but like any system created by man, it was subject to the influences of nepotism, corruption, and greed.  In some ways, it may even have been too stable, as it laid the basic foundation for feudalism in medieval Europe.

Second, the system was designed to ensure that no military claimant to the throne could mount an effective challenge to the emperor.  Creating redundancy in administrative offices, layers of authority between the provinces and the throne, and subordinating the generals to the civil authority, were all ways of preventing an over-ambitious general from seizing the throne.  Diocletian and Constantine had learned their lessons well.

Military Organization

Diocletian and Constantine also reformed the military organization of the empire.  The main development here was the separation of the military into two spheres.  One part of the military focused exclusively on guarding the frontiers of the empire, and was garrisoned in a specific place to perform this function.  Another part of the military was a mobile force, deployable at the emperor’s command, that could respond to crises wherever needed.

The mobile forces were called comitatenses, and the garrison forces were called limitanei.  The limitanei retained the size of the old Roman legion (6000 men), but the legion was frequently subdivided and moved around as needed.  The privileged units of the comitatenses were known as the palatini; these were normally stationed in Constantinople or in Italy.  The palatini seem to have inherited the functions of the old Praetorian guard during the Principate.

Infantry units were composed of units known as auxilia; cavalry units were grouped separately in units of 500 called vexillationes.  Infantry and cavalry forces were sharply separated.  Constantine began the practice of appointing two commanders of the military forces:  the magister equitum (master of horse) and the magister peditum (master of “foot” or infantry).  These military titles eventually were both called magister militum (master of soldiers).[8]

As the empire expanded and aged, the old principles of its composition were gradually modified or abandoned.  Recruits came more and more often from the ranks of foreigners, especially Gauls, Sarmatians, and Germans.  This fact would be one of utmost significance for the fourth and fifth centuries.  Declining birthrates in Italy could not meet the need for new bodies to fill the ranks of the army, and so the emperors were forced to rely more and more on Germans.

These men would inherit the Roman army, and then eventually the empire itself in the West.  The army was in theory democratic in the sense that any conscript could rise up through the ranks to become a high-ranking officer. (We find the same mobility in the military caste of the Mamlukes in the Ottoman Empire centuries later).  A list of Roman military offices and definitions can be found in Appendix B.

Besides its military forces, Rome also enlisted the help of client states along its borders to keep out hostile raiders.  These states were called foederati, after the Latin word for treaty (foedus).  Examples of such states were the Arab tribes bordering Persia and the Ethiopians south of Egypt.  As time went on, such foederati would even supply with Rome with military units; so we find that some Arab tribes asked to join Julian’s Persian expedition.

Naval forces were generally neglected.  Rome was not known for its great interest in maritime power projection, and navies tended to be built as the occasion called for.  After the seventh century, the eastern empire would eventually become the major naval power in the Mediterranean in response to the existential threat it faced from the explosive force of Islam.

Social And Ecclesiastical Organization

The social life of the empire in this period was marked by authoritarianism and the increasing reliance on compulsion to maintain social stability.  On the large farms, the latifundia, the labor of slaves or serfs began to replace the old independent tenant farmer.  Constantine decreed that tenant farmers were bound to the soil, as well as their children after them; thus was the groundwork laid for medieval serfdom in Europe.

A serf was not even permitted to leave his geographic area without permission.  In the guilds and trade professions, sons were required to follow the occupations of their fathers.  On the local level, municipal governments decayed for want of good men to participate in them.  The duties of municipal administration were formerly considered an honor, and something that an ambitious man might aspire to.  These so-called curiales were now drafted to do the unpleasant work of enforcing imperial decrees, which might include such things as tax collection and the levying of troops.

As the responsibilities of these curiales increased, fewer good men were willing to assume the posts.  Unable to protest and lacking any meaningful imperial representation, the gentry of the provinces often had no recourse except to join the army, join the Church, or in extreme cases, move into barbarian lands.  Here again, the emperors after Diocletian solved the problem by forcing the curiales to remain in place and follow orders; they and their sons were bound to the land.  Compulsion became the rule in social organization.

In the early centuries of the Christian era, the Church existed as a parallel organization alongside the civil and administrative institutions of the empire.  It at first shadowed the institutions of the empire; then it co-existed uneasily with them, borrowing many of their features; and finally, in the West at least, it replaced the imperial institutions altogether in the centuries after Julian.  In the East, ecclesiastical structures always remained firmly subordinated to the authority of the emperor.

Church organization began with groups of believers congregating together in units known as ecclesia, or “gatherings.”  Priests were chosen to lead these groups, and over time it became necessary for a bishop to assert control over these priests.  Over time, more complex offices such as archbishops or primates were needed to control bishops.  Eventually, the clergy came to segregated into a hierarchy of seven distinct orders:  bishops, priests, deacons, subdeacons, acolytes, exorcists, and readers.[9]

Ultimate figures of authority were the so-called “patriarchs” who sat in the major metropolitan centers of Constantinople, Antioch, Rome, and Jerusalem.  Formal meetings of bishops and archbishops (called synods or councils) could be called by the emperor or a patriarch; such meetings could be provincial, plenary (specific to either the East or West), or general (representing both East and West).  There was a subtle but persistent cooperation between the imperial and ecclesiastical authorities:  each needed the other, and came to rely on the other.

In the early centuries of the Church, the rise of schisms, heresies, and disorders necessitated the intervention of the imperial authority as a mediator; and, in turn, the emperors came to rely on the Church’s wonderfully efficient social services and local administration.  The relationship was thus symbiotic.

In every age, figures of authority have found it useful to enlist the loyalty of spiritual institutions as a means of maintaining social order.  It was remarkable, in the West at least, how smoothly and subtly the imperial functions were transformed into Church responsibilities.

In this respect we observe one of the eternal truths of  social tectonics:  institutions are what they have to be, in order to respond to the challenges of their period and place.


[1] Ricciotti, Age of Martyrs, p. 5.

[2] Crispus was cherished by his father, but likely the victim of palace intrigue involving his stepmother, Fausta, who wished to remove him from the scene to make way for her own offspring.  Fausta spread malicious gossip about Crispus, which resulted in his trial and execution.  When Constantine found out he had been duped by Fausta, he had her executed.  So the wicked are ensnared in the traps that they set for others.

[3] These informers were called agentes in rebus, or “official agents.”  The agentes were led by the magister officiorum (master of officials).  This secret fraternity was originally established in the second century as a benign office that looked something like a quartermaster.  Under Diocletian and his successors it transformed into a secret police force.  See Rolfe, note 2, p. 98.

[4] See Bury, p. 15.  In theory, a new monarch could be proclaimed by the force of the public will.  If such a proclamation was backed by sufficient power, it could be carried through to conclusion.  The Eastern monarchy was, in practice, not as absolute as one might suppose.

[5] Bury (p. 22) tells us that one house, built by Constantine, was located near the imperial palace, and the other was near the forum.

[6] Id. at 23.

[7] In the east, the title of vicarius was replaced by the term comes orientis, and in Egypt it was called the praefectus augustalisSee Bury, 27.

[8] Rolfe, p. xxxiv.

[9] Bury, p. 64.


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One thought on “Civil And Military Organization Of The Later Roman Empire

  1. Have you read Joseph R. Peden’s “Inflation and the Fall of the Roman Empire?”

    It’s skewed with a libertarian bent, but one of the things he talks about is that the growth in all these separate authorities sapped the Roman economy and led to increased financial hardship, hampering somewhat the reforms instituted by Diocletian and Constantine to stabilize the financial system which suffered grievously also in the 3rd century.


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