Late Roman Army - seniores and iuniores

[Robert Vermaat]

I've always found the idea of legions splitting up and bits of them being sent to opposite ends of the empire rather troublesome - it would be very difficult to organise, amongst other problems!

[..]

I'm sure somebody's suggested this idea before - I'm still combing through the literature on the subject! But does it sound plausible? One problem with it might be the position of the auxilia palatina units, who have no 'original' unit to draw upon. A second enlistment from scratch might be an option though.

Talk about a geriatric thread!  

Some problems with your hypothesis:
1- Legions were constantly being split up and sent to different parts of the empire - vexillations had been sent to wars and sometimes never returned.
2- If I went along and agreed with a vexillation becoming an independent unit (I'm sure that happenened), how about another vexillation being split off afterwards and in turn becoming an independent unit? How would you distinguish that one from the parent unit (your 'seniores') and the first split-off (your 'iuniores') if it was that important to distinguish between them? We know that some legions were being split up in larger or smaller units during this period anyway, possibly ending up with 'new legions' of cohort or double cohort size, permanently stationed or moved to other parts of the empire (such as Legio V Macedonia). yet your system would only allow for the parent unit and the first split-of to be distinguishable as 'seniores' and 'iuniores'.

Of course it's possible that some splits inti sen/iun started this way, that cannot be excluded. But as a system that ended up with mostly only 2 names combined in this manner, I doubt that your suggested mechanism was behind it. My favorite remains a separeted cadre which was then fleshed out.