APA (7th ed.) Citation

Collins, R. (2009). Keepers of the keys of heaven: A history of the papacy. Basic Books.

Chicago Style (17th ed.) Citation

Collins, Roger. Keepers of the Keys of Heaven: A History of the Papacy. New York, NY: Basic Books, 2009.

MLA (9th ed.) Citation

Collins, Roger. Keepers of the Keys of Heaven: A History of the Papacy. Basic Books, 2009.

Warning: These citations may not always be 100% accurate.