Late Roman Army Grade/Rank List under Anastasius

[Nathan Ross]

how are we sure that a biarchus is limited to scholae and palatinae?

Sorry, my omission - I meant that these ranks were confined the the new cavalry units (both Equites and Scholae) and the auxilia. Your XI Dalmatorum would be a cavalry vexillation, of course.

[Edit - I see you've added some more examples! But all of them are cavalry or auxilia, except perhaps the numerus scutarii - although the schola scutariorum were probably cavalry, so these could be too...]

This theory rests on some very limited evidence, however! - mainly that the ranks of biarchus, circitor, centenarius and ducenarius appear in inscriptions to the equites, scholae and auxilia palatina but not (as far as I know) in the legions, which seem to have continued using the old (centurio) ordinarius and optio ranks.

I'm still not sure that the centenarius commanded a century. The only examples that we have... seem to point at salary, not command over an amount of something

Originally, I think, both centenarius and ducenarius related to the old equestrian pay grades. These, possibly, were later used to distinguish centurions or other junior officers promoted to the Protectores or to command in the comitatus (this idea suggested, I think, by Hepworth in 'Studies in the Later Roman Army); only later, and for some completely unknown reason (!) did they appear as small unit commanders in the cavalry and auxilia. Perhaps because these units were already part of the comitatus? Don't know...

There are some inscriptions to centenarii in the auxilia though - CIL 05, 08740: [Fl]avio Andiae centenario numeri bracchiatorum ;
CIL 05, 08745: Fl(avius) Diocles ce/ntenarius n(umeri) Ib(er)orum - both from Concordia and dated cAD400.

[Edit 2 - cavalry as well: CIL 13, 01848 - Fl(avi) Ingenui / centenari(i) ex num(ero) eq(uitum) / cataf(ractariorum) sen(iorum) ; CIL 05, 08758 - Fl(avius) Roveos centenarius de equitum comitum / seni(orum) sagit(tariorum) ]

These certainly look like rank titles to me - it's only an assumption that they indicated command of a unit, although Vegetius suggests the rank was equivalent to the Ordinarius.

Vegetius mentioned a tribunis minor, which might signify a change in promotion procedured, or he might have had the vicarius in mind.

I would think so, yes. There's no vicarius listed on the Perge inscription, of course (or a primicerius - or, more troublingly, a aquilifer or other standard bearer for the whole unit...) so the tribunus minor seems to be filling that role.