I took Rome as the Turks around turn 80 or something. I declared a Jihad on the city and sailed there, made it there from Constantinople in about three turns. Love those Jihads.
As soon as I took it, the Pope declared a crusade on Rome. At least 10 or 12 stacks of crusaders came toward the city, most of which I defeated outside the city, and on that little bridge right next to Rome. Once the crusade failed, I declared a Jihad on Milan and took that. Then, they declared another crusade on Rome, so more catholics come my way, though less this time. By the time I had seized Milan and Bologna, I had destroyed most of Milan's military power in italy, so the rest of the region was easy to take.
Now, things have settled down, it's probably been 100 turns since I took Rome, and the pope doesn't stay alive long enough to call any new crusades since I kill him every turn. The Milanese and Moors are still trying to push me out, to no avail.
Basically, when you take Rome, expect a TON of crusader armies to come your way in retaliation. It would be smart to attack Rome with a very strong force of your best troops - don't send greens, or be a bit more tactical and wait till a Crusade is already in progress on another target before you attack Rome, that will the city will be easier to hold.
Oh, and make sure you take Palerno castle too, you'll need it to reinforce your guys around Rome. The closest castle to Rome besides Palerno (in Sicily) is Innsbruck, WAY to the north in the mountains.
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