After developing my 6th Century Byzantine army, which was the basis for an earlier column, I decided to update my Later Roman army. I had recently purchased sufficient figures for a Patrician Roman army so there was scope to make lots of interesting units/formations. This was in turn prompted by my reading of several books, which I had borrowed form a friend and were all recent (2-3 years old) publications.

Two titles were particularly helpful: Warfare in Roman Europe by Hugh Elton, and The Late Roman Army by Dixon and Southern. Both books included new research on the later Roman military. The most interesting chapters were those concerning organization, weapons, armour and tactics.

I also had my own copy of "Roman Military Equipment" by Coulston and Bishop. This was supplemented by an article by Coulston, "Later Roman Armour 3rd-6th Centuries AD" taken from the Journal of Roman Military Equipment Studies (JMRES 1, 1990).

There were a few other helpful titles, albeit much older and therefore did not include the most recent information. These are listed in the bibliography.

While all these books and articles were useful, I still felt that there was a bit of a vacuum concerning the specific troop types and unit organizations. The later Roman military is now considered to have been composed of many specialist units divided into several categories, and their equipment and arms reflected their ability to fight and operate in diverse ways. So I decided to compile a general army list in which I could identify the various organizations.

Starting Point

The army of Constantine the Great was used as the start point for this list as this was the first distinct model upon which to base the list. It could be argued the army was developed by Diocletian but some of my secondary sources, such as AHM Jones, suggest that he enhanced rather than changed the existing military forces. Several articles in the Journal of Roman Studies debated this point and I refer interested gamers to them.

The development of the Late Roman Army is usually taken to be the result of 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 3rd 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 earlier empire 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 frontier provinces and were stationed on the perimeter of the Empire. The entire establishment was 450,000-600,000 men, at least on paper.

In both field and border forces, the manoeuvre units were the same. Roman officers commanded legions, cavalry and auxiliary infantry units. Infantry dominated the army numerically and these formed the basis of tactical doctrine throughout this period. From the late fifth century, cavalry became more important on the battlefield, but infantry still made up the bulk of Roman armies. Naval units, engineers, medical services, intelligence services and a full logistical service supported the land combat troops.

In addition to regular units, the Romans made increasing use of contingents of barbarian allies. These were used to supplement Roman forces, but also as a military necessity. To take Roman units 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.

Constantine is generally credited with the creation of the standing field armies and the border forces. The former were developed to give the senior military commanders and the emperors armies which were mobile. Pre-Constantinian forces had normally been assigned to specific areas and contingents (vexillationes) were withdrawn from them to create temporary field forces for a campaign. The limitanei were the remnants of the older formations still assigned to specific areas, mainly along the empire's frontiers.

There has been much written about the distinctions between the comitatenses and limitanei, however, I shall not delve into this topic. Both would be of interest to gamers and should merit our attention. The field armies were the main participants in the major battles and campaigns, while the border forces took part in many skirmishes, minor battles and cross-frontier operations. The division of the Later Roman military permits players to choose units from the comitatenses for large scale tabletop armies or from the limitanei for small scale forces.

Detachment System

One way of looking at the restructuring of the army is as a formalization of the detachment system. Prior to the development of field armies, units were often ordered to send detachments or vexillationes to an ad hoc army for specific operations. These detachments could also be grouped by a local commander, such as a provincial governor, from units under his command.

The one apparent advantage of this system was that it permitted units to retain garrisons in its assigned area. This was important to ensure that frontier security was maintained, albeit at a reduced level. In 84 AD, the legions of Britain were required to send detachments to the Emperor Domitian for use in his campaign against the Germans. Each legion provided between 1000 and 2000 troops for this campaign. The provincial governor, Gnaeus Julius Agricola, was still able to form a provincial field force for his campaign in Scotland against the Caledonians. It can also be presumed that some troops were left as garrisons at each legionary base and other normal stations. (See Saga December 1998 for details of Agricola's campaign.)

Using this example, there is a precedent for dividing legions into three separate sub-units:

central field army under the emperor;
provincial field army under the governor; and
garrison forces.

It is likely that these were not equitable divisions of the legions as the requirements for troops were different. The emperor could drawn upon all his forces and selected detachments from several provinces for his central army. The governor would have fewer resources than the emperor but still need a large force for a campaign of conquest (estimated at 20-30,000 troops by historians). The garrison forces could be fairly small, as the province of Britain was relatively quiet during this period. Assuming that each of the four legions was close to full strength (about 5000) and that the emperor took between 20 and 40%, the governor had 60 to 80% for his campaign army and garrisons.

If he used a small force for garrisons, say about 20%; he would have between 2000 and 3000 per legion or 8000-12000 troops for his field operations. To this total, he added auxiliary units (8,000 infantry and 5,000 cavalry). So Agricola could have had 25,000 troops for his provincial field force. Other sources state that Agricola took elements of only three legions, which may have reduced this total but still gave him with a fairly large army. As long as troops were not routinely engaged in major operations, field armies could be formed by drawing detachments serving in quiet areas and combining them with troops stationed near the campaign area. Major offensive campaigns could be undertaken when enemies at two or more locations along the extensive frontiers did not beset the empire. Units were transferred throughout the empire, either for specific campaigns or to garrison new conquests or particularly troublesome areas. In addition, new units could be raised for specific operations and then retained as garrison forces or disbanded. The legions tended to be retained until either suffering heavy losses or siding with the loser in a civil war.

There were no reserve forces established either for offensive or defensive operations until the Emperor Septimus Severus garrisoned one legion in Italy to augment the Praetorian Guard in the early 3rd Century. The Emperor Gallienus established a mobile cavalry force at Milan in the late 3rd Century and used this for many of his campaigns.

3rd Century

In the 3rd Century, the Roman armies were involved in various civil wars, foreign and domestic campaigns, and divided amongst several rival rulers (Palmyra, Gallic empire of Postumus and rump of Roman Empire). This is also the period when field armies began to become more permanent fixtures within the military.

Commanders required two basic organizations:

a garrison force to secure lines of communication and protect the "home" territory;
and a field force capable of operating at long distances from this "home" territory.

The original reserve/mobile forces were regularly augmented by detachments grouped into field armies in the 3rd and 4th Centuries. Many of these detachments evolved into independent units either because of their long-term attachment to the field armies or to distant provinces. They may not have been created as permanent units, which may explain why they did not have the same strength as previously established units. This is particularly true of the legions. In the 3rd Century, they had a paper strength of 5500.

This figure had been reduced in many legions to 1000-1200 over the next century (if one accepts the general consensus view of historians that legions had reduced in size). An alternate interpretation is that the various sub-units may have totaled 5500 (again on paper rather than an actual strength), although they operated independently. This may explain why the various legions retained similar names to that of the "parent" unit.

This is plausible because new units were given distinct names. There may have been one exception in which units belonging to a usurper or defeated rival emperor may have been incorporated into the victorious army under a new name. If this were the practice, then historians would be hard pressed to show the relationship between a parent unit and one of its independent detachments.

So the practice of creating detachments from legions evolved from a temporary expedient to a formal system. The division of the army into comitatenses and limitanei led to the creation of several legions sharing common names and numbers. Some of these may not be apparent in their close association because of the use of nicknames or locations in their formal titles. Other identifiable links were lost because of name changes as explained above.

More Late Roman Army

Late Roman Army: Introduction
Late Roman Army: Weapons
Late Roman Army: Personal Organization
Late Roman Army: Bibliography
Late Roman Army: Sources and Terminology
Late Roman Army: Military Organization
Late Roman Army: Unit Sizes and Types
Late Roman Army: A Model Army
Late Roman Army: Painting Tips
Late Roman Army: Bibliography