Cohort commander?

[popularis]

Tribunus militum as a praetorian commander: do you have a reference for this? I'd expect tribunus cohortis x praetoriae.

Fully correct, thats what I expeceted, too. But, if I remember right, I have read the short term Tribunus Militum naming a praetorian tribune, if it is absolutely clear from context, that he is a praetorian.

Would that be Virgius Marsus?

AE 1978, 286 = AE 1996, 513 (Marruuium, Regio 4, Italia)

A. Virgio L. f. Marso / prim(o) pil(o) leg(ionis) III Gallicae / iterum praef(ecto) castr(orum) Aegy(pti) / praef(ecto) fabr(um) tr(ibuno) mil(itum) in praet(orio) / diui Aug(usti) et Ti. Caesaris Aug(usti) / cohort(ium) XI et IIII praetoriar(um) / IIIIuir(o) quinq(uennali) delato hon/ore ab dec(urionibus) et popul(o) in col(onia) Troad(ensium) / Aug(usta) et Marru(u)io testamento / dedit uicalibus Anninis imagin(es) / Caesarum argentias(!) quinque / et sestertia X milia / uicales Annini{s} honor(is) / causa

An interesting inscription, but not uncontroversial I rather side with Keppie in suspecting that whoever in Marruvium was responsible for the inscription made a mistake!

EDIT: I'm an idiot who doesn't read his own notes. And I'm answering my own question. Anyhow, there's also L. Ouinius Rufus:

CIL 10.4872 = ILS 2021 (Venafrum, Regio 10, Italia).

L. Ouinius L. f. Ter(etina) Rufus / prim(us) ordo cohortium praet(oriarum) / diui Augusti prim(us) pil(us) leg(ionis) XIIII Gem(inae) / trib(unus) mil(itum) cohort(is) XI urb(anae) trib(unus) mil(itum) / coh(ortis) [.]III praet(oriae) praef(ectus) fabr(um) IIuir / L. Ouinio M. f. Ter(etina) patri / M. Ouinio L. f. Ter(etina) Vopisco fratri / Allidiae L. f. Rufae matri / Pulliae Primae uxori

So yes, tribunus militum is perfectly acceptable as a commander of a praetorian or urban cohort. I suspect that over time the title was elided in the same way that command of a cavalry cohort was:

tribunus militum cohortis x praetoriae -> tribunus cohortis x praetoriae
praefectus equitum alae x -> praefectus alae x

a vexillatio of roman citizens, which is supposed to fight (not just move) had the need of a commander who is a (ex-)magistrate elected by the people of Rome. So just some of the higher tribunes were that experienced.

You're right about this being off topic. But prefects of non-Senatorial rank could command Roman citizen troops, it's just that they didn't usually do it.

Of course you can write a 200 page book just about the equestrian career, and some guys did.

200 pages, pfft, weaklings. Demougin is probably still the best analysis of the equestrian cursus in the early Empire, and her first major book and accompanying catalogue alone is about 1600 pages