Late Roman Unit Sizes

[Nathan Ross]

The 6000 man legions that Vegetius speaks of appears to be 6000 men per legion

Yes, he says they 'had 6000 men apiece' (I.17). He then goes on to talk about Diocletian and Maximian coming to the throne, so the numerical figure is pre-tetrarchic; the emperors renamed these legions Herculiani and Ioviani 'and preferred them to all other legions'. This is possibly Vegetius's gloss on the tetrarchic foundation of legions I-VI Jovia and Herculia - as we know that at least two of the Herculia legions had ten cohorts, these were possibly all traditionally-sized legions (unless a 'cohort' meant something different by this point?)

a nice, neat number that divides into the magic 2400 figure for Seniores and Iuniores!

I confess that I'm not especially a believer in magic numbers of any sort in this debate! I suspect that unit sizes were fairly random within certain parameters (and probably had been throughout Roman history...) The relative differences in unit nomenclature - between a 'cohort' and a 'legion', for example - from the 4th century to 1st might be more useful to try and establish... But that doesn't help much... ;-)

apart from the Augustian legion, all the rest of the units are Cohorts, so the legion could well have been over 2000 men strong.

Actually I tend to think that none of these units are cohorts - Claudian is using poetic terms. The Ioviani and Herculiani are palatine legions, the rest are palatine auxilia, each an auxilium or a numerus... whatever that means!

11,600, which is only 400 short of the claim by Ammianus that Julian's army only numbered 12,000 men in total.

13,000, according to A.M. 16.12. The Primani might have numbered 6000 at full strength, but I'd suggest that it had been a long time since a full legion had taken the field anyway - a strong detachment would have been more likely, even if we aren't talking about a new-style smaller legion...