Wanted to throw this out there, I posted it in another thread a few months ago.
Planning versus fortification: Sangallo's project for the defence of Rome:
http://www.fsgfort.com/uploads/pdfs/Public/Pepper F2 P.pdf
Basically these were some of the first really gigantic gun resistant fortifications to be designed after a Turkish fleet held a dagger over Rome. Instead the Turkish fleet was just loading up on water from the Tiber and moved on. The Pope wanted a gigantic series of defenses and many fortification experts throughout Christendom came to these meetings to discuss the cities fortifications. Designs for cannon resistant fortifications already existed, but the act of putting so many designers in one room really purified and standardized the designs which later made it in other parts of Europe.
The designs were largely abandoned, I think only a tiny section was built. Part of the problem was that it was expensive as balls and would have left parts of the city undefended despite its massive cost. So in the end much more limited defenses were built around the Vatican at a later date.