I note with the Marian reforms you can recruit auxiliary cavalry in many of the provinces you have. Looking at the RV, there's a good spread of them.

One question, however, are they recruit-able only through your factional barracks? And if so, does that mean you have to have a type II government in place to recruit them (and thus be able to build that barracks)?

I ask because that's not going to fit too well with my slow Romanisation process, where I usually put a type IV (or more recently, due to client ruler issues, type III) government in place for a while before upgrading 30 years later.

I'm thinking specifically of a conquest of Gaul, which historically wasn't immediately Romanised (though it did happen quite fast in comparison to other places) and getting Germanic auxiliary cavalry to use in my campaigns there.