Amy Welborn discusses Fallen Order: Intrigue, Heresy, and Scandal in the Rome of Galileo and Caravaggio (hardcover) by Karen Liebreich.
Any contemporary relevance or parallels? "Hmm."
I still have to get Cities of God (hardcover--$65!!!) for its portrayal of medieval politics and Italian city states, of which I know very little. Certainly they would offer an alternative model of Christian polity to the Christian kingdoms and feudal arrangements of the same time.