As far as I can tell the 3 roman factions are based around the triumverate of Caesar (Julii), Crassus (Brutii), and Pompey (Scipii) and the roman civil war. I guess I'll find out for sure in 2.5 weeks . According to http://www.totalwar.com/ the Scipii can build a shrine to saturn and that a coliseum gives Velite, Samnite, and Mirmillo gladiators. 1 gladiator type per roman faction as has been said.