Auxillary Recruitment

[AK]

I know that Auxiliary soldiers were recruited from non-Roman tribes, but what exactly does non-Roman mean? Does it mean not from the city of Rome itself or the Empire in general? Like for example if someone was born in Gallia, would they be recruited as a legionary or auxiliary? Would it depend on if they were born after Rome conquered said country?

Thanks.

[LuciusSallustiusPlautus]

Not all Auxilia where non-Romans. Cohors II Italica was made up of Roman citizens to assist in Germany I believe, but while it was up there it recruited some locals.

[Lupianus]

Basically, auxilia of the 1st to 3th century AD were recruited from non-citizens for the most part. That is to say from people who did not have Roman citizenship, but would have a chance to get it via military service (if they lived to be honourablly discharged). Citizenship was inheritable, so any legitimate offspring of a Roman citizen would be a citizen as well. However, it was not bound to a specific place of birth. So, to confuse things further, inhabitants of Rome or Italy would not have been necessarily Romans citizens.

Some auxilia units received citizenship as a whole for distinguished service, acquiring the title "civium Romanorum" (of Roman citizens). Any new recruit thereafter, though, didn't automatically receive citizenship as well.
By 212 AD all (free) inhabitants of the Empire received citizenship, although the minutia and impact of this law are debatable. Certainly, in the aftermath the difference between citizen and non-citizen units within the army got blurred.

We better not touch on the different grades of citizenship beforehand. This legal stuff is pretty confusing.