This article is an edited transcript from Roman Legionaries with Simon Elliott, available on History Hit TV.
At the beginning of the Principate (27 BC), powerful Roman dynasties managed to rule the Roman Empire for numerous decades – perhaps most famously the Julio-Claudian and Flavian dynasties. Yet as the Imperial period went on, Emperors started to come and go quite regularly and it became quite hard for an emperor to not only establish legitimacy but then gain legitimacy for his descendants.
So how big a role did the army play in this growing difficulty? And did they become a cause for instability?
Not just a fighting force
The Roman military, as most if not all militaries are throughout history, were ‘other’ when compared to the rest of society; they were within society but were ‘other.’ They were not just a fighting force for external threats; they were also the sharper end of the policing force within the empire and also administered the empire as well, which meant that they actually functioned as part of the judiciary.
Occasionally the soldiers clearly were a force of instability, not always, but occasionally they were. The crisis of the mid-third century is a great example as many things went wrong within the empire during this time, part of which was internecine warfare between contenders for the throne and contending imperial lineages.
Instability in Britannia
One of the best examples about this sort of instability is with regards to the Roman province of Britannia – the farthest point from the centre of the Roman Empire, the furthest from Rome. The Romans had never conquered the north and west of the Island and they therefore needed an exponentially large military presence there all the time.
If you look at the Severan campaigns in Scotland for instance, Severus had a force of 60,000 men. Think about that. The modern British army is 80,000 men strong. Severus had a force of 60,000 men, the kernel of which was this embryonic field army which he created, and he arrived in Britain with his 60,000 men in a population of 3.5 million.
Meanwhile the modern British army is 80,000 men in a population of 65 million. So the Roman army was therefore not just other; it was a significant other.
Furthermore in Britain the army was furthest from Rome. If these military forces for whatever reason were idle or if the military leaders or the governor or the procurator had reason to be worried about what was happening in Rome, then there was therefore always going to be the chance of usurpations. On many occasions this became a reality: Constantius, Magnus Maximus, Magnentius.
Postumus dragged Britain into his Gallic Empire, but the only one which actually worked was Constantine the Great. He was declared emperor by his troops when he was in York after the death of his father. So it was always a possibility that the soldiers could be a cause for instability.
Keeping the soldiers busy
Nevertheless there were long periods of stability in the Principate. The reign of Antoninus Pius is a great example of that; but the Roman military was always there and if it was not kept busy doing what its day job was and if it was then around people who had some kind of grief with what was going off elsewhere in the empire it was always a risk that something could happen that was untoward towards the ruling imperial family.
This was why the emperor was always trying to keep the Roman military busy doing things if they weren’t fighting.