The Late Roman Army, 284 - 410 CE by Salah ad-Din

The Roman Emperor Diocletian (r. 284 - 305 CE) has been hailed by some historians as a "second Augustus". Like Augustus, Diocletian used both tact and brute force to shape the world as the Romans knew it into his own image. He too had emerged at the top after nearly a century of civil strife, incessant warfare between Roman legions. And, like Augustus, he left his sucessors with a very different Empire than that of his predecessors.

The Roman Army at the beginning of the 4th Century, unsurprisingly, was a very different force that those that had marched under Augustus, or Trajan, or even the Severans. There is no evidence that it's quality as a potent fighting force, capable of both defensive measures and offensive campaigns, had declined. But it was an army that had spent the past century destroying itself, all for the sake of the ambitions of ambitious officers.

The Roman Army of the Third Century

There is very little information available on the Roman Army in the half century between the death of Severus Alexander (235) and the ascension of Diocletian (284); most of what we do know is gleaned from surviving inscriptions, and recent archaeological efforts at ancient forts and battlefields.

In this era, the classic distinction between legions and auxiliary cohorts was fading away. Antoninus "Caracalla" had awarded Roman citizenship to every free person living in the Empire in 212, thus taking away the traditional definition of an auxiliary soldier. Inscriptions show that the auxiliary units continued to operate under their old names until the final decades of the 3rd Century, but now their ranks were filled by men coming from the same background as recruits into the legions.

The Third Century also saw the increasing usage of smaller infantry units. After the First Century it became rare for new legions to be raised; those legions already in existence were stationed predominately in fortresses along the more sensitive frontiers, the Rhine, the Danube, the Euphrates, as well as Britain and north Africa. The surpression of minor raids and insurrections were left to the auxiliary units, while legionary manpower was reserved for wars of conquest - which effectively ceased past the reign of Trajan.

When Marcus Aurelius fought against the Germanic incursions of the 160s and 170s, he raised two new legions, but much of his manpower was drawn from detachments of legions already in existence. It was far safer and more practical to snatch a cohort out of every Rhine legion, for example, than to pull an entire legion off the frontier and leave it vulnerable to the enemy. The armies of Marcus Aurelius, Lucius Verus, and the Severan emperors were made up not of several legions, but instead a multitude of these vexillationes - so-called because they marched under a flag called a vexillatio in Latin.

A vexillation of 500 or 1000 legionaries was a far handier unit, both tactically and strategically, than the ponderous bulk of a full-strength legion. As a result, by the middle of the Third Century the vexillation had effectively replaced the traditional legion in its place in Roman military organization. By the end of the Third Century, many vexillations had developed names and unit personalities of their own, having long abandoned the notion of ever being returned to the parent legion, which may well have been on the other side of the Empire.

The Romans probably never thought in strategic terms as modern nations and armed forces do. But their attitude towards the defense of their provinces definitely changed over the violent course of the Third Century Crisis. Cavalry and light infantry units enjoyed increasing prominence in this chaotic decades, and emperors began to establish their seats of government at more strategic locations - Sirmium, Mediolanium, and Antioch, among others. Inscriptions strongly suggest that local militias also increased in numbers, and experience, during the Crisis. While the legionary units were off killing each other in civil wars, it was up to the common provincial to defend his farm and village from barbarian raiders.

As early as Septimius Severus (193-211), the emperors started maintaining what were in effect, private armies. The Severan emperors stationed theirs in Rome and the neighboring town of Albanum. By the reign of Gallienus (259-268), Mediolanium (Milan) had been chosen for this purpose, as it was closer to the Rhine and Danube frontiers. By the end of the Third Century, the Praetorian Guard was effectively reduced to garrison duty in Rome herself; elite legionary vexillations and cavalry units had replaced it in forming the Emperor's comitatus.

The Empire and Army of Diocletian and Constantine

Diocletian is best-known for establishing the Tetarchy, which lasted in one form or another from 293, when he adopted his former comrade Aurelius Maximianus as a co-ruler, to his own abdication in 305. The Roman Empire was divided into eastern and western halves, each ruled by a senior and a junior emperor (Augustus et Caesar). Ultimately this system proved a failure; Diocletian's retirement was rapidly followed by more civil strife was was not effectively ended until the rise of Constantine's brutish, one-man regime.

The Roman Empire of the Tetarchs seems to have been a darker place than the Empire of previous centuries; at the least, it would have looked very unfamiliar to Augustus or Marcus Aurelius. Diocletian not only divided the Empire between himself and his colleagues, he also divided each of the provinces into many smaller units, each with its own governor and small garrison. Diocletian's motives for the reorganization of the Empire were likely diverse, but it is clear that he did not want any of his governors having access to too many soldiers at once. At this aim, he succeeded; his regime, though hardly bloodless, saw much less rebellion and civil war than the half century of Crisis preceding it.

At Diocletian's ascension, it is unlikely that any of the legions were in one piece. The word "legion" itself was not disposed of, but it came to have the same meaning that "vexillation" had a century before. The typical infantry unit now appears to have numbered somewhere between 300 and 1200 soldiers, and was commanded by an officer with the rank of praepositis or tribunus. Praepositi had commanded vexillations in the previous century, while tribunes had been serving as legionary officers and commanders of auxiliary units since the late Republic.

How many men served in the Roman Army at the turn of the 4th Century? Modern scholars are generally of the opinion that the Army increased in numbers - traditionally it has been assumed that it may have doubled under Diocletian. There are certainly a number of legions that appear to have had their origins in the reign of Diocletian. However, just as Diocletian created many new provinces without conquering any new land, he appears to have created many, smaller military units without significantly increasing the number of soldiers. It is modernly estimated that around 390,000 men served in Diocletian's army; as opposed to the 440,000 men of the Severan army, when the Empire was at its peak.

Guard Units

The Equites Singulares Augusti - the Emperor's cavalry guard - disappears from our sources in the Third Century. The Praetorian Cohorts are greatly diminished in importance and prestige after the fall of the Severan Dynasty; by the ascension of Diocletian they appear to have merely formed a garrison force for Rome and the surrounding region. They were disbanded altogether by Constantine after his victory at Milvian Bridge in 313 CE; the Second Parthica Legion, the only legion stationed in Italy in the Third Century, continued to exist, but its barracks in Albanum were donated to the Church.

Under Diocletian, the "new" Praetorian Guard took the form of the twin units known as the Ioviani and the Herculiani, named for Diocletian and Maximian who associated themselves with Jupiter and Herakles respectively. Founded in the mid-late 290s, these were probably an infantry force raised from crack legionary forces.

Under Constantine, there arose a replacement for the Singulares - known as the Scholae Palatinae ("Guardians of the Palace"). These regiments appear to have been elite cavalry, and lasted well into "Byzantine" times in the East. They appear to have been the primary, if not only guard unit for much of the time period discussed here. "Palatina" was used as an identification for any elite unit in the 4th Century, in the field army as well as the comitatus.

Comitatenses and Limitani

The regular troops of the 4th and 5th Centuries appear to have been divided into two grades - comitatenses ("of the Comitatus") and limitani ("of the frontiers"). The comitatenses are generally viewed as an "elite" force by modern scholars, whereas the limitani are viewed as a poor quality militia. There is actually little contemporary evidence for these stereotypes; both types of soldiers appear to have been well armed and disciplined, and more than capable of facing any foe, Germanic or Persian.

The distinction between the comitatenses and limitani is that the latter were, at least in practice, a local force, operating in their province of origin. The comitatenses appear to have been billeted on the civilian population the major cities of the Empire, and were called up when the Emperor was on campaign (e.g. Julian's Germanic and Persian Wars). Limitani who were drafted, often against their will, into armies going on the offensive for foreign campaigns were, perhaps mischeivously, termed "pseudocomitatenses".

The legionary fighting style, though it had changed in many regards, was visibly recognizable in the 4th and perhaps even 5th-6th Centuries. Ammianus Marcellinus' accounts of Julian's Wars would be just as at home in a First or Second Century account. At the Battle of Strasbourg, he refers to legionaries as crouching behind their shields "like gladiators" and trading swordstrokes with Alammanic warriors. The comitatenses and limitani alike fought with broad oval shields, likely flat or only slightly concave, and medium-length cut-and-thrust swords. Most also carried a clutch of javelins, though there is evidence to suggest that thrusting spears were becoming more popular in this period.

Light troops were prominent in the 4th Century and were likely drawn from all ranks. As in previous centuries, many were proper legionaries stripped of their body armor and perhaps their helmets. Soldiers fighting in light marching order had always featured in Roman warfare; in this era they were commonly used for commando-like raids on enemy settlements. The soldiers of the Late Roman Army appear to have actually been much more flexible than their predecessors, even if their training was less comprehensive.

Cavalry

Most modern scholars are of the opinion that the cavalry of the Roman Army increased both in numbers and prominence over the course of the 3rd and 4th Centuries. Many of them appear to have been cataphracts equipped in imitation of Persian heavy cavalry; such men were armored from head to toe, rode armored horses, and carried an array of weapons including lances, swords, and composite bows. Many wore mail aventails of a sort that would seem more at home in the medieval Middle East; Ammianus relates that cataphracts at Constantius II's triumphal parade were thought to be "not men, but statues" by the people of Rome.

Horse-archers were a novelty in the Roman army before the 4th Century. Even in the 4th and 5th Centuries many of them appear to have been mercenaries, variously of Persian, Sarmatian, or Hunnic origin. Egyptian papyri dating to the reign of Diocletian show that there was at least one unit of horse-archers operating in the province. In comparison to the more impressive cataphracts and their ponderous lance-charges, horse archers receive little attention in most of our sources.

Discipline

The 4th Century Roman Empire was a state ruled by paranoid and ruthless men, who were in turn represented to the common people by vicious and untrustworthy bureaucrats. The Roman Empire had never been known for going easy on law-breakers and trouble-makers, but from the time of Diocletian onwards the penalties imposed on such people were often as sadistically inventive as they were harsh.

In the 4th Century, deserters were executed by burning (crucifixion having been outlawed upon Constantine's converstion to Christianity). Conscripts were often branded on their faces or right hands to reduce the odds of attempted desertion. Draft-dodgers were often so desperate as to cut off their thumbs, rendering themselves unable to hold weapons and fight effectively. Some emperors ordered the execution of such men, others decreed that they be drafted anyways.

That said, the soldiers of this time period, especially the comitatenses, appear to have gotten away with much more than the legionaries of previous generations. Soldiers billeted in major cities were particularly known for their abusive treatment of their guests, helping themselves to food, supplies, and the bodies of their hosts' wives and daughters. In terms of organization, logistics, training, equipment, and tactical expertise, the Roman Army was still the finest in the Mediterranean world. Only in discipline, and occasionally the command talent of its leaders, does the 4th Century Roman Army sometimes fail to impress.

There is no evidence for the length of service required of a recruit, past the third quarter of the Third Century. It is unlikely that the 25 years of service demanded in the earlier days of the Empire were shortened by Diocletian or Constantine. It was probably Diocletian who published the Edict demanding that the sons of soldiers enlist in the army upon reaching maturity. Many officers in this period were the sons of common soldiers.