The Evolution of the Roman Army Part V — The Diocletian Reforms and the Late Roman Army
Just a note before I begin this post, I must give everyone a heads up that we are entering into the last final two centuries of the Western Roman Empire. From here on out when I refer to the “Roman Empire” I’m mostly going to be referring to the west rather than the east. I’m not going to continue this series by moving onto the army of the Eastern Roman Empire, aka the Byzantine Empire, which survived the fall of the west in 476 for another thousand years. To do so would make an eight post series into a 16 post series, and I aint gonna do that. Also I don’t know that much about the Byzantine Army. If anyone would like to pick up where I left off, let me know. If it’s good stuff I would be happy to reblog it 😀
When I left off with the previous post, Rome was more or less in it’s golden age. That would all change with what historians would call “the Crises of the Third Century”. Between 235 – 285 AD the empire would enter a tumultuous phase in which it would be embroiled in near constant civil war, foreign invasion, and political intrigue. Emperors came and went, some whose reigns barely lasted a few years before they were overthrown, assassinated, and replaced by another emperor. Pretty much any Roman general with a few legions to his command declared himself emperor and sought to seize the power. Entire provinces would break away from the empire, forming their own kingdoms and independent realms. The crises of the third century would end in 285 AD with the reign of Diocletian. By then the empire was thoroughly devastated, thus Diocletian sought a number of reforms to stabilize and rebuild the empire. The Diocletian Reforms were widesweeping, affecting every aspect of Roman life including society, the economy, government, and of course the military.
With the Diocletian Reforms the Roman Army would see a vast change in both strategy and tactics. The first major reform was the elimination of the regular legions and the auxiliary. By the reign of Diocletian, there was little difference between the inhabitants of the provinces and the Romans themselves. Most provinces throughout the empire had been thoroughly “Romanized”, and thus the provincial inhabitants were culturally similar to the average Roman citizen. There would have been few cultural differences between, say, a Gaulic provincial, and the average Joe Roman living in central Italy. Secondly in 212 AD the Emperor Caracalla had declared universal citizenship for all free inhabitants of the empire. No longer were there Roman citizens and provincial subjects, now everyone was a Roman. It no longer made sense to have separate legionary and auxiliary units. Thus the legions and auxiliary were disbanded and reformed into new integrated legions. The amount of men in each legion was lowered from 5,000 men to 1,000 men, creating smaller tactical units which were more flexible strategically and in the field.
Roman infantry units were divided into two main groups; the comitatenses and the limitanei. The comitatenses were the regular rank and file infantry of the army. However, unlike the earlier legions, the comitatenses were stationed well behind the Roman border, occupying populated areas such as the towns and cities. Those who were stationed at the border were the limitanei. Unlike the comitatenses, the limitanei were light infantry who were lightly armed and armored. This system involved a new “defense-in-depth” strategy. Whereas before the empire’s strategy was to station the bulk of its troops at the border who would deal with problems at the border, now the empire was betting on a system of layered defenses. The role of the limitanei was to guard and police the border, often dealing with enemy raids as well as bands of brigands and bandits. In the case of a full scale invasion, the limitanei were not to directly engage the enemy as they were not conventional combat troops. Rather, the limitanei were to either hole up in fortifications and keep the enemy in one place, or slow down the enemy advance through a guerrilla war consisting of surprise attacks, ambushes, and delaying actions. Once the limitanei had sounded the alarm that trouble was afoot, the comitatenses would form armies that would march out and deal with the invaders. This new defense in depth better allowed the army to focus men and resources to particular hotspots, rather than stretching the army out among various border outposts, requiring long supply lines stretching hundreds of miles through wilderness areas.
Originally the limitanei were full time professional soldiers like the comitatenses. However, over time most limitanei units would become permanent residents. They began intermarrying with the locals, forming small villages, and planting crops to supplement their income. In this way the limitanei evolved from professional soldiers to landed residents and militiamen. The limitanei were armed with a short sword, dagger, spear, a few javelins or archery equipment, a circular shield, and helmet. Typically the limitanei lacked armor, being light infantry who needed to move quickly and act at a moment’s notice. Whereas the comitatenses were regular infantry, the limitanei were more like independent corps of self sufficient frontiersmen and minutemen. One could imagine news of a Goth raid occurring at the border, and the limitanei scrambling from their homes and gathering their equipment to go out and chase down the raiders. On the regular battlefield, limitanei were often attached to comitatenses units as light infantry support, becoming known as pseudo-comitatenses.
Unlike the limitanei, the comitatenses were heavily armed and armored. Typically the comitatenses infantryman was armed with a spear, a long sword called a spatha, a dagger, and a round shield. Where as the limitanei were typically unarmored, the comitatenses wore mail armor and in some cases scale armor.
Unlike earlier legions, the comitatenses no longer carried javelins, but instead used darts (plumbata) which could be clipped inside of a shield. They would throw their darts at the outset of combat, with the rear ranks continuing to rain darts upon the enemy after close quarter combat had begun.
In battle the comitatenses used tight formations, locking their round shields together into a tight shield wall with spears facing towards the enemy. Often they would form a double shielded formation called a fulcum which involved the front two ranks, one standing and one kneeling. Usually a regular shield wall formation was used while advancing, while the fulcum was a stationary defensive position. It wasn’t uncommon for light infantry armed with bows or javelins to act as front line skirmishers, much like the velites of the earlier maniple system. Before the regular infantry made contact with the enemy, they would harass the enemy by raining volleys of arrow and javelins upon them. They would then retreat to the rear of the shield wall, continuing their harassment of the enemy from relative safety.
Recall that in the previous post the Roman’s relied upon looser infantry formations. Now, it almost seems like the army is regressing way back to the days of the ancient phalanx from the very beginning of this series. There are actually very good reasons for this change, and it was not because of the “barbarization of the army”, the theory that a large influx of “barbarians” into the ranks of the army caused the army to adopt barbarian equipment and tactics leading to a breakdown of the tactical complexity of the army. This is a topic which I plan to cover in a separate post. Rather the reasons for this tactical change are much more practical in nature. First the tactical and strategic mindset of the army changed from that of an aggressive offensively minded army to a defensively minded army. Long gone were days of Roman expansion, now the main purpose of the Roman Army was to defend and protect. On a tactical level, Roman units no longer assaulted the enemy as a standard tactic, but would occupy advantageous ground, form a solid defensive formation ,and let the enemy come to them. The second reason why the Romans made this change was the adoption of new heavy cavalry units by their enemies. In the 3rd century the Great Migration period would begin, and Germanic tribes from northern and eastern Europe would arrive on the scene, familiar peoples such as the Goths, the Vandals, and the Burgundians. With them they would bring new breeds of very large horses, horses which were much larger than those fielded by the Romans. In the Middle East, the Persians were ramping up their use of horse archers and cataphracts. Cataphracts were heavy cavalry units which were armed with lances and equipped with heavy armor.
With the increasing use of heavy cavalry, the loosely formed cohorts were no longer effective, being easily ridden down and broken up by “barbarian” cavalry and cataphracts. Thus, stronger and tighter phalanx-like formations were needed to repel heavy cavalry charges. The short gladius lacked the reach needed for an infantryman to deal with a mounted foe, thus it gave way to spears and long swords. The rectangular scutum was ditched in favor of round shields, because round shields when locked together in a shield wall provided gaps through which spears could poke out.
In reaction to the increased use of enemy cavalry, the Roman’s too would increase their number of cavalry units. In addition, like the phalanx of ancient times, these new formations lacked mobility and were very vulnerable to enemy flanking maneuvers. Thus more cavalry units were needed to guard Roman flanks. The Romans would also adopt heavy cavalry formations such as cataphracts, however the Roman’s never utilized cavalry to the extent of their enemies, such as the Goths, Vandals, Huns, or Persians. Heavy infantry would remain the backbone of Roman strategy and tactics.
A third type of unit within the Roman Army were the palatini, who were elite soldiers recruited from among the rest of the army. The palatini made up the personal army of the emperor, and usually numbered around 20,000 – 30,000 soldiers. Among the palatini were a unit of cavalry called the scholae. Numbering around 5,000 – 6,000, the scholae were the personal bodyguard of the emperor, replacing the role of the Praetorian Guard after their disbanding by Constantine.
Finally, there were the foederati. The foederati were foreign or “barbarian” units which were attached to the Roman Army. Foederati swore allegiance to the empire, either because of treaty after being defeated or by convenient alliance. While foederati were technically part of the Roman Army, they had their own commanders and in reality owed the empire little loyalty. One day the foederati could be friends to the empire, the next day they could be enemies. Especially since the empire often treated their foederati allies poorly. As the empire declined the Roman Army depended more and more on foederati units, until by the last few decades of the empire the foederati made up the vast bulk of the army. Most foederati units adopted Roman equipment and tactics, and were trained by the Romans. They were not the half naked war painted, disorganized screaming barbarians as depicted in popular media, but would have been heavily armed and armored, using tactics and formations that were as complex as those fielded by the Romans. Thus, foederati who decided to turn against the empire could be exceedingly dangerous.
With the Diocletian Reforms the Roman Army would be expanded to the point that it numbered around 600,000 men by the reign of Constantine the Great. By the mid 4th century the empire had unofficially been divided between east and west (officially in 395 AD), with around 300,000 men occupying each half. Despite an increasingly stagnating economy, a dying corrupt government, and waves of barbarian invasions, the Western Roman Empire would still scrape up enough cash and resources to maintain a strong, well equipped, and well trained army. That would change around the turn of the fourth century after a series of military disasters, and the incompetent reign of an emperor known as Honorious “the Dipshit”.