Dr. David Gwynn

One of the difficulties here, the original model for the Roman emperors, the one that emerged under Augustus way back at the turn of BCAD, was the idea of the princeps.

So the Roman emperor as the first among equals.

That as an ideology was already largely dead by the end of the second century.

It was buried in the third century crisis.

These people are military emperors, almost all the third century emperors are.

So they're not so worried about that old imagery.

But they do actually still want to be able to receive those petitions, if only because that's how you know if things are going wrong.

Yes, because Diocletian once again took a look at the third century.

What were the lessons learned during that 50 years before he took power?

That included the fact that you needed smaller army units that were more flexible, could more easily respond to crises, and you need cavalry.

The Romans had never been as strong on cavalry as they had been on infantry, but in the 3rd century the need for a good cavalry arm became more and more apparent.

And the 3rd century emperors who tried to resolve the crisis, like Gallienus and Aurelian, this is what they were developing.

Diocletian took a look at those developments and set about trying to work out a more systematic pattern.

So you get a marked increase in the number of legions, but it doesn't actually mean there's a massive increase in the army because the size of a legion seems to have been significantly reduced.

So whereas the classic Roman legion, the one you see in reenactments, the one that goes back to the late Roman Republic, 5,500 men in a legion becomes more like 1,000.

And that's on the evidence of the army camps that Diocletian and the other Tetrarchs build along all the major frontiers.

Diocletian's looking at the infrastructure, the roads, the camps.

So we get told by one particularly hostile source, that's the Christian Lactantius, that every Tetrarch wanted a larger army than any emperor had had before, so the army must have therefore increased four times.

There's no earthly way the Roman army increased four times from its old rough estimate of, say, 300,000, because there's no way the Roman Empire can support a million men in the army.

The modern estimate, I think, would be that there is an increase in the number of soldiers, just not anything like as drastic as Lactantius is claiming, but perhaps up from 300,000 to 350,000 to perhaps 400,000.