Which army was better – the early imperial Roman army, or the late Roman army?
Picture two boxers: one is a younger guy, his face is a mess of scars, his shoulders and gait confident, thick neck and wild eyes; you get the sense that no number of knockout punches would floor him. The other is an older guy, his face is also scarred, he’s a little warier and more calculating than the first guy, with a killer right hook, but you get the sense that outlasting him just might win you the fight.
This is how I would compare the Roman army of the Principate days, the early empire, to the Roman army of the Dominate days, the later empire.
I hear this idea often: the Principate army must’ve been better than the Dominate army, because the Principate army kept the Roman Empire safe, while the Dominate army failed to stop the Empire falling apart.
But how valid is this idea? Lots of writing and discussion focus on issues like equipment, training, and morale. Here we’ll steer away from that, we’ll be looking at the bigger picture, on the strategic level.
I’ll say that it’s not a matter of which army was better; it’s that the two had very different backgrounds, different natures. One was malleable, the other was brittle. Both the Principate and Dominate armies could throw killer knockout punches at their opponents; but while the Principate army could take knockout punches, recover, and knock out its opponent in turn – it was malleable – the Dominate army couldn’t take hits that well, at times avoiding battle, and taking a long time to recover from major defeats – it was brittle.
On the surface of it, the Principate and Dominate armies had a lot in common: the core of both armies was the armoured infantryman, trained and paid by the state; his immediate superiors were often professional officers, while the senior officers varied between career soldiers and politicians doing their stint in the army. He had to carry around his own food and gear, which was annoying, but it was all part of the army’s highly effective logistics system which ensured he wouldn’t starve to death on campaign.
But the differences show on the strategic level.
The Principate army was malleable. One thing you’ll notice when looking at Roman military history is the number of times the Roman army got absolutely thrashed: there’s the infamous Battle of the Teutoburg Forest against the Germans; the Battle of Rhandeia against the Parthians; the Battle of Beth Horon against the Jews; and Domitian’s Dacian War, just to name a few. In each of these cases the Principate suffered a crushing defeat, losing anything between one and three legions – and bear in mind that the Principate only ever had about 30 legions.
And yet in each of these cases, the Principate was able to recover and take the fight back to the enemy: Roman forces under Tiberius crossed the Rhine again a year after Teutoburg; Roman forces under Corbulo marched right back at the Parthians after the defeat at Rhandeia, forcing them to negotiate, and a generation later Trajan even occupied the Parthian capital of Ctesiphon; a year after Beth Horon Nero sent four legions to crush the Jewish rebels; and it may have taken more than a decade, but Roman forces under Trajan marched back against the Dacians and annexed their kingdom.
The pattern we see here is short term disaster followed by long term victory.
And in fact if we jump earlier back in time we’ll see the the armies of the Roman Republic doing similar things: just look at King Pyrrhus if-we-win-one-more-time-against-the-Romans-we’re-dead of Epirus, and Hannibal, who could butcher some 50-60,000 legionaries in one afternoon at Cannae, and keep slaughtering Romans for the next decade, and still lose the war.
Again there’s that pattern of Roman forces absorbing blow after blow, and still delivering a knockout punch at the end. They were malleable. They could take a hit, and then hit right back.
But this is not what we see with the Dominate army. Don’t get me wrong, on balance it still won most of its fights, but looking at its performance you definitely get the sense it was less able to recover from disasters, and, related to that, less willing to aggressively engage the enemy.
A list of major Dominate military disasters might go something like this: the Siege of Amida against the Persians; Julian’s Persian campaign ending in the Battle of Samarra; the Battle of Adrianople against the Goths; if you want we could count the sack of Rome; and the Battle of Cape Bon against the Vandals.
In each of these cases, military disaster sent the Dominate reeling: Roman forces were in fact able to push back against the Persians after Amida, but this opened the doors to Julian’s disastrous Persian campaign, and the ensuing loss of Armenia; the defeat at Adrianople meant the Goths would stay a thorn in Rome’s side for a long time; and the defeat at Cape Bon, with its catastrophic loss of manpower and loss of any chance at recovering Africa with its grain, pretty much doomed the Western Roman Empire.
The pattern we see here is different; the Dominate army could throw knockout punches just as well as the Principate army, but unlike the Principate army, the Dominate army seemed to lack the ability to take knockout punches first before following up with its own. It was brittle, where the Principate army was malleable; knockout punches would send it reeling, struggling to recover.
But something else is going on in the background in the world of the Dominate: a whole mess of civil wars which ended up killing eight of the 30 or so emperors between Constantine and Romulus Augustulus; and the strange cat-and-mouse game between Stilicho and Alaric in the Balkans, as opposed to Stilicho simply crushing Alaric.
And where we jumped back in time from the Principate days to see how its strengths were similar to the strengths of the Republic, we’ll jump back in time from the Dominate days to see that its weaknesses are a product of its predecessor, the Empire of Third Century Crisis.
The Roman Empire of the third century had nearly imploded, torn apart by civil war. Roman emperors learned one important lesson: keep your soldiers close at hand because only they can protect you, and pay them well or they’ll murder you. The Dominate army needs to be seen in that context, as the product of the Third Century Crisis: it was as much a military force as a political tool in a way that the Principate army by and large was not (barring a few major incidents).
Which brings us to the issue of civil wars and the sparing use of manpower: the Dominate army was needed not only to fight barbarians, but almost just as importantly, to fight internal usurpers. So why throw your best troops at the enemy when you need them for personal protection? Why risk battle at all if it means risking precious troops? This goes some way to explain why the best troops, the praesental troops, were kept close to the emperor; it might also explain why elite field armies were stationed at major cities, leaving the day to day defence work to the lower-status border troops. The Dominate army wasn’t supposed to take knockout punches, because the emperor needed it for safety. It couldn’t be used very hyper-aggressively.
So the Dominate army appears less aggressive because its job seems a lot more complicated than the Principate army; and as manpower grew scarcer, as relations between the Western and Eastern empires got less friendly, it only acted more and more cautiously. Which is possibly why Stilicho played his cat-and-mouse game with Alaric instead of destroying him, and why the Romans were never really able to destroy the Goths after the Battle of Adrianople, instead using them first as key allies at the Battle of the Frigidus, then hiring entire communities of them as federate troops after that. The Western Empire certainly wasn’t able to kick out any of the barbarian communities which crossed the frozen Rhine in AD405, and had to accept that they were in the Empire to stay. That was the first of many knockout punches that took out the Western Empire for good.
So which army – Principate or Dominate – was better?
Again I’ll say it’s not a valid question to ask. The two armies lived in different worlds, and in some ways had different jobs, because they had very different natures – one was malleable, the other brittle.
The argument that the army of the Principate preserved the Empire while the army of the Dominate lost it doesn’t make much sense; after all, what do we make of the army of the Eastern Empire, which was recognisably the army of the Dominate, fighting Constantinople’s wars even after Rome fell? This was the army that retook Rome under Justinian and saw off the Persian threat once and for all under Heraclius, only falling finally to the rising power of the Muslim Arabs.
Maybe the best we can do when answering this question is to think about context. Different contexts give different meanings, different roles. When looking into the past you might find familiar strengths, familiar weaknesses, but looking forward you might find unexpected weaknesses – the army of the Principate evolving into the flesh-tearing army of the Third Century – and unexpected strength – the army of the Dominate protecting Constantinople for more than a hundred years after the fall of Rome.