This chapter was inspired by the histories of the Commune of Rome and of Cola di Rienzo, a very interesting historical persona, contemporaneous of Petrarch, if i'm not mistaken. In these two episodes, the Pope and the aristocracy were expelled from the city, and a communal regime inspired in the Roman republican ideals was established, the first one being fairly long-lived for its convenient alliance with the Holy Roman Emperor. Both episodes fascinate me, so i decided to put something similar in the narrative.
http://en.wikipedia.org/wiki/Commune_of_Rome
http://en.wikipedia.org/wiki/Cola_di_Rienzo
The in-game explanation: the readers will surely remember that King Godwin I created an Antipope, and at the time i explained that the only way to get rid of one of them is to press his claim to the Papacy and establish him in Rome. The very existance of an Antipope is a modifier that reduces the "Moral Authority" of the Catholic Church. At 1250, in this chapter, it was lower than 20%, meaning heresies sprung up everywhere, and are impossible to be get ridden of. So i declared war against the Pope, conquered the Papacy and installed Pius II, the Saxon pope, so Moral Authority can rise again.
I felt i couldn't explain this in narrative, so decided to transform the war against the Pope in a war against Rome itself

, and took inspiration from the Commune of Rome.