Emerging from the Third Century Crisis, the Roman Empire and its military underwent a cultural revolution of colossal breadth. The era before the transition is recognized as the ‘Principate’ – i.e. rule by the First Citizen – and the era after as the ‘Dominate’ – i.e. rule by despot. This evolution was necessary for the autocracy of the Roman central government, because of the unremitting dynastic chaos of the Third Century Crisis. The architects of the revolution were the Emperors Diocletian, and Constantine.
Diocletian created an institutional division between civil and military offices – beforehand the two had often been fused – increased the administrative capacity of the central government, and humbled the Roman aristocracy. Constantine sought to unify the state under a single religious faith – Christianity – as well as establish an enduring administrative division between the Greek East and Latin West of the Roman Empire by founding a second capital city – Nova Roma or Constantinople – with its own Senate. Ian Hughes chronicles all of these events in his book, but with special attention given to the revolution in military affairs which took place under the two Emperors.
“Modern estimates suggest that the number of legions probably doubled between the reigns of Severus and Diocletian, and by the time of the Notitia Dignitatum (early-fifth century) the 30 legions of the Early Empire had grown to more than 200.
“It has been noted that cavalry only has a ‘strategic mobility’ – the ability to march and retain the capability to fight effectively – that is superior to infantry over short distances. Over longer distances – for example, any march taking around a week or longer to complete – cavalry actually have a lower mobility due to the need to rest the horses, so in reality their strategic mobility is actually less than that of infantry. These questions have resulted in the whole idea of a ‘mobile cavalry force’ being seriously doubted.
“The chaos and confusion caused by piecemeal reforms and temporary solutions to short-lived problems in the third century resulted in the Roman army becoming a disorganized and inefficient organization. Despite it winning many battles in the third century, it was hardly capable of protecting the frontiers from the ‘Germanic’ tribes to the north, the Sasanid Persians to the east or even the Blemmye to the south.
“…it is possible to infer that both Maxentius and Daia offered better pay, higher donatives and better retirement benefits than their opponents. However, the fact that these troops were still easily defeated at the Battles of the Milvian Bridge and Tzirallum suggests that, despite the financial benefits, the troops’ opinion of their emperors was low. The further implication is that, rather than being generous, in order to retain their troops in their service the two emperors had little option but to increase their pay and benefits… It is the morale and readiness to fight and die for their emperors that were the main reasons for the victories of both Constantine and Licinius, not Constantine’s access to new types of troops.
“Their ability to plan and finance large-scale military campaigns, alongside their ‘sound and sophisticated logistical organization’, was only equaled by the capabilities of the Sasanid Persian Empire. Rather than simply attempting to defeat an enemy or conduct a raid, the Romans were capable of ‘having goals, knowing routes, terrain and the type and strength of the opposition’, meaning that their campaigns could be focused and their intended outcome clear. Of equal importance, they could gain intelligence concerning enemy location, direction and intentions, either through the means of informers or from the fact that an army on the move deployed a screen of light cavalry to gain information and screen the main body as it marched.
*All excerpts have been taken from A Military Life of Constantine the Great, Pen and Sword.