Cohort commander?

[Nathan Ross]

Legionaries... could well have simply been under the control of their own centurian or did he and they come under the control of the resident unit commander during their stay.

There's a letter by Fronto, I think, which suggests that an auxiliary praefectus cohortis and a centurion were equal in pay and rank. He probably means those centurions directly appointed ex eques, who may have been paid more than the risen-from-the-ranks variety.

So the prefect and the centurion sharing the same fort could have been equals, in fact, although the prefect may have tried to pull social rank if the centurion was not an equite!

In the empire you have Tribuni which have been promoted from praefectus cohortis. Of course these guys could do that job after 3 years of experience. What scares me more is, that people without any military experience at all did start as praefectus cohortis, if just of equestrian rank.

There were also 18-year-old centurions! ;-)

Some men did start the tres militiae auxiliary command early (there's a selection aged 18-23 or so), but many more began in early middle age after a civil career, often as a town councillor. Still not military experience, but it would have provided a grounding in projecting authority.

The youngest known (equestrian) legion tribune was aged, I believe, 28 - but they served on until their fifties in some cases, and several died in battle.

Undoubtably they had some command function on occasions - leading subunits either in battle or on detached expeditions. But, as we've said, this doesn't translate into an 'official' cohort-leadership role.