Here's one so self-evidently compelling on its face that you can't imagine why nobody thought of it before. It's Anthony Majanlahti, The Families Who Made Rome, subtitlted "A History and a Guide." Think about it: you atour the ancient parts of Rome, you operate in terms of political figures: here Augustus, here Trajan, here Constantine. When you do the much more extensive Renaissance elements, you're usually working in terms of the artists--Bernini, Bramante and suchlike. But all those Renaissance piles have a political history behind them, not least in the sense that somebody had to stump up the money. Here the sources get there due: the Colonna, Della Rovere, Fernese, Borghese, Barberini, Pamphlij, Chigi and suchlike who provided the gold to make it go.
Majanlahti has structured it as a tour guide. I haven't had the opportunity to use it that way yet but I must say that it works pretty well as an informal general of the age. In crude summary, then: what we have here is an odd sort of hybrid government perhaps like nothing so much as the Roman republic, where a network of rich and powerful clans jockey for position so they can line their private pockets with public wealth--and for "private pockets," read "lavish public display."
The standard pattern has an almost tedious regularity: get one of your clan elected pope; let him cooperate with his "nipote"--the "nephews" (sometimes, actually nephews)--and set the family up for life. Oddly enough, you didn't get a second short (the della Rovere were an exception)--but properly engineered, one was as good as forever.
It occurs to me also that we see a grand tradition unveil itself here. We boring northerners sometimes make fun of their Italians for their skill at turning public resources to the service of private greed. I think in particular of Ed Banfield's superb Moral Basis of a Backward Society where he displayed the physical and spiritual poverty of a "community" (if you can call it that) without any sense of civic virtue (here's a review I wrote of Banfield's book a while back). The interesting modifier here is "backward;" read Majanlahti for an account of the same kind of self-serving in a society that is not "backward" by any conventional definition.