Historically Primus marched on Rome and defeated Vitellious at the battle of cremona while Vespasian remained in the east.His son Titus conquered Jeruselum.But Primus is locked for 100 turns and Titus is'nt on the map from what I can see.Not having played it yet just per-using{just can't find the time} the map at the beginning does Primus get released by event and titus appear by the same?
The number of turn's would seem to preclude this,when Vespasion came to Rome it was not at the head of an army for Vitellious was already dead and he had been proclaimed emporer by the senate
I apologize if answering this is a spoiler just curios.