Roman army rankings?

I’ve been reading some books about the end of the Roman Republic and got to thinking about the movie Gladiator. Now, if he was a Spaniard, how high a rank could he have a acheived in the Roman military? Did the Roman ranking system work differently in Imperial times? I’d guess he was a legate, but that required being a citizen.

To keep this more factual, how did the ranking system work in the Roman army?

http://members.tripod.com/~S_van_Dorst/Ancient_Warfare/Rome/hierarchy.html

Also, the fact that the character was a “Spaniard” doesn’t mean that he wasn’t a Roman (I haven’t seen the movie, so I don’t know the circumstances). The various Hispanias were Roman provinces, and Roman citizens lived there. In fact, there were some emperors born in Spain, such as Trajan and Hadrian, as well as at least one would be emperor (he claimed the throne and didn’t get it), Magnus Maximus (which I always figured was a pretty arrogant cognomen)