Citazione Stile APA (7a Edizione)

Cheetham, N. Keepers of the keys: A history of the Popes from St. Peter to John Paul II.

Citazione stile Chigago Style (17a edizione)

Cheetham, Nicolas. Keepers of the Keys: A History of the Popes from St. Peter to John Paul II.

Citatione MLA (8a ed.)

Cheetham, Nicolas. Keepers of the Keys: A History of the Popes from St. Peter to John Paul II.