You start as a republic before Marius reforms to the army. Its basically how you started the first Rome Total War.
but eventually, in the course of the campaign, the marian reforms will occur? and when does the campaign end? east/west schism? or fall of WRE?
Does thar mean you have 300 turns to achieve one of the victory conditions or 300 turns until you can't play anymore?
300 turns to win, and also, after 300, there will be no more events