Late Roman Army - seniores and iuniores

[Steven James]

If we accept that a legion under Diocletian was around the 6000 man mark, and by 500AD a legion was between 1400-1700 men strong (if using the evidence from the Perge fragments), then it may be plausible for the legions to have been split into three approximately 2000 strong legions under Constantine, which over time may have come down to the legion size described in the Perge fragments.

Except you need to add to the 6,000 iuniores the 1,200 seniores in the tribal system and then divide by three.