Zodiac and Late Roman Army Organisation

[Robert Vermaat]

It's worth noting Mommsen's precise wording here [ with my comments ]:
"the legion normally numbered 6,000 men [ really? ] and stood under six tribunes [ but surely there were differences between the senatorial tribune and the five equestrian tribunes? ]; it seems reasonable to divide it into sixths [ but this has no relevance for Diocletian's army; even in the fourth century, it is not a universal phenomenon: in the ND, XIII Gemina and II Adiutrix are divided into six, but others are divided into fewer fragments (or none) ] and assign each tribune partial command over 1,000 men [ can this be demonstrated to have happened? ever? ]"

In this case, please do not mistake Nicasie's ideas for those of Mommsen's - this reference was about who said what. Of course Mommsen should be read with care - this is the late 19th centurey after all, and the man did rewrite sources when he thought it better to.

So did a legion number 6000 men? Well, some did, Vegetius is the last one telling us so, and we have to decide whether that was right or not.
What has relevance for Diocletian's army or not I can't possibly say. I an not of the opinion that Diocletian altered the Severan army in it's entirety and that Constantine did it all over again. I think that Diocletian began a development which was carried out by Constantine, and that Constantine did his own thing: it's very hard to say who did what and to which extent. But some legions may well have remained untouched even after Constantine, and were split up later.
Can we prove that a legion was split up and each tribune assumed command over a new part of 1.000 men? No we can't, as we do not have a letter from HQ to command this. But we know more or less who commanded smaller legions and units, and therefore it's perhaps logical to assume that, in the very case of a split-up of such a legion (and we can't tell exactly how that went about), these tribune retained command of such units.