Italy in the Thirteenth Century Volume II (Boston-New York, 1912) Mazzi-Belli, V., "Pietro Hispano papa Giovanni XXI," Rivista di storia della medicina 15 (1971), 39–87 (in Italian) Morceau, Joseph, "Un pape portugais : Jean XXI, dénommé Pierre d'Espagne", Teoresi 24 (1979), 391–407 (in French) Maxwell-Stuart, P. G. Chronicle of the Popes: The Reign-by-Reign Record of the Papacy from St. Peter to the Present, Thames & Hudson, 2002, p. 119. . Jean Claude Bologne: La Naissance Interdite ; stérilité, avortement, contraception au Moyen-Age. Orban, Paris, 1988 . Joachim Telle: Petrus Hispanus in der altdeutschen Medizinliteratur und Texte unter besonderer Berücksichtigung des Thesaurus pauperum‘. 2 vol., Heidelberg, 1972. External links J. P. Kirsch: Art. Pope John XXI (XX), in: The Catholic Encyclopedia, Vol. VIII (1910) Salvino Leone: Joke Spruyt: Peter of Spain (2001), in: Stanford Encyclopedia of Philosophy Popes John XXI Bishops of Braga Cardinal-bishops of Frascati 13th-century Roman Catholic bishops in Portugal 13th-century Latin writers John XXI John XXI John XXI John XXI Academic staff of the University of Siena Viterbo Papacy 13th-century popes