1. The Bad Popes, Chamberlin, E.R., Sutton History Classics, 1969 / Dorset; New Ed edition 2003.
2. The Pope Encyclopedia: An A to Z of the Holy See, Matthew Bunson, Crown Trade Paperbacks, New York, 1995.
3. The Papacy, Bernhard Schimmelpfennig, Columbia University Press, New York, 1984.
4. L