Pope John XXI (; – 20 May 1277), born Pedro Julião (), was head of the Catholic Church and ruler of the Papal States from 8 September 1276 to his death on 20 May 1277. Apart from Damasus I (from Roman Lusitania), he has been the only Portuguese pope. He is sometimes identified with the logician and herbalist Peter of Spain (; ), which would make him the only pope to have been a physician. Early life Pedro Julião was born in Lisbon between 1210 and 1220 to Julião Pais Rebolo, a physician, and his wife Mor Mendes. He started his studies at the episcopal school of Lisbon Cathedral and later joined the University of Paris, although some historians claim that he was educated at Montpellier. Wherever he studied, he concentrated on medicine, theology, logic, physics, metaphysics, and Aristotle's dialectic. He is traditionally and usually identified with the medical author Peter of Spain, an important figure in the development of logic and pharmacology. Peter of Spain taught at the University of Siena in the 1240s and his was used as a university textbook on Aristotelian logic for the next three centuries. At the court in Lisbon, he was the councilor and spokesman for King Afonso III in church matters. Later, he became prior of Guimarães. He was Archdeacon of Vermoim (Vermuy) in the Archdiocese of Braga. He tried to become bishop of Lisbon but was defeated. Instead, he became the Master of the school of Lisbon. Peter became the physician of Pope Gregory X (1271–1276) early in his reign. In March 1273, he was elected Archbishop of Braga, but did not assume that post; instead, on 3 June 1273, Pope Gregory X created him Cardinal Bishop of Tusculum (Frascati). Papacy After the death of Pope Adrian V on 18 August 1276, Peter was elected pope on 8 September. He was crowned a week later on 20 September. One of John XXI's few acts during his brief reign was the reversal of a decree recently passed at the Second Council of Lyon (1274); the decree had not only confined cardinals in solitude until they elected a successor pope, but also progressively restricted their supplies of food and wine if their deliberations took too long. Though much of John XXI's brief papacy was dominated by the powerful Cardinal Giovanni Gaetano Orsini, who succeeded him as Pope Nicholas III, John attempted to launch