I’vve also been pondering the strength and overall organization of the Late Roman Army. Warren Treadgold argues that the expansion and the split between field and frontier forces occurred in the reign of Diocletian. Others such as AHM Jones argue that they came later.
Zosimus reports figures for the strengths of the armies of Constantine and Maxentius in 312, and Constantine and Licinius in 324. These are too high to account for the field armies alone. These seem to refer to the total strengths, field and frontier, of 4 different armies, and then the heavier naval forcees, and then the lighter ones. They add up to 645,000 personnel, and Agathias also reports 645,000 in the old Empire.
Treadgold suggests that Zosimus has dug up figures for Constantine, Maxentius, Licinius, and Maximinus Daia in 312, and has creatively reinterpreted them as strengths for Constantine, and Maxentius, in 312, and Constantine again, and Licinius, in 324. But this gives Maxentius by far the largest army. My suspicion had been that there were permanent field armies, of around 130,000 people total, hat these were grouped with the Praetorian Guard, and that Zosimus had assigned them all to Maxentius because of that.
In this list, Zosimus gives Maxentius 188,000 people. Zosimus elsewhere gives Maxentius 120,000 people, and the Panegyrici Latini gives him around 100,000. So it’s likely that this list overstates Maxentius’s strength in some fashion.
But Jones and other historians make clear that the basic distinctions in Diocletian’s reign were between the legions and vexillationes, on one hand, and the old auxiliaries, on the other. There aren’t enough Praetoriani, Lanciarii, Scolae, Comites, etc. to account for 130,000 people on the, uh, other other hand.
It seems most likely that Zosimus’s figures refer to the forces of Crispus, Constantine I, Constantine II, and both Licinius I and Licinius II.
Yes, Constantine II was only 8 years old. I guess his father wanted his son to get an early start, and trusted his aides to offer good advice.
This solution to the “problem of Zosimus” leaves the problem of the organization of the Late Roman Army between Diocletian and Constantine completely unsolved.