Re: Marian Reforms
The trigger for the Marian reforms is either building an Imperial Palace in one of your cities (because it allows the recruitment of Praetorians who are a post-Marian unit) or building 5 army barracks in any 5 cities.
In Vanilla Rome, the Marian reforms are unique for Roman factions and only give them additional units; I'm not sure what Darth may have done with them but historically they revolutionised the Roman army, turning it into a more professional force with state-provided equipment.