Or just have a fascination in carving a world empire. For me, I almost always play to the finish of the short campaign, or about ten regions after that, and quit when I have regional dominance. But I normally play my Roman campaigns to the finish of the long campaigns, possibly a bit beyond that. One reason is the civil war and the Marian reforms-- the Roman late-game remains interesting, and there's a kind of satisfaction in surpassing the historical Roman empire. Another is because the Romans have it much easier than any other faction when it comes to keeping public order up. Arenas and, later hippodromes, combined with prudent farm management, can keep even the largest cities reasonably content well into the late-game.