Peter of Spain, Pope John XXI

Portugal (1215-1277). Born Peter Juliani, the man who would eventually become Pope John XXI earned a well-deserved reputation as the eminent 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 Summulae Logicales was used as a university textbook on Aristotelian logic for the next three centuries.  One of his most important medical works was Liber de oculo (“Concerning the Eye”), possibly written while he was a medical professor at Paris. A copy of this influential book was found three centuries later among the papers of Michelangelo, who had taken the time to copy out the entire book himself. The book’s last paragraph was undoubtedly of deep value to the artist: “When something falls into the eye, make a wash with honey water and rose water and milk.” For a man who spent endless months looking up at the ceiling of the Sistine Chapel as he worked, Michelangelo would certainly have found such a remedy useful.

Peter was Archdeacon of Vermoim (Vermuy) in the Archdiocese of Braga, then became the Master of the school of Lisbon. Peter soon moved to Rome, where he became the physician of Pope Gregory X (1271–76) 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).

After the death of Pope Adrian V on 18 August 1276, Peter was elected Pope on 8 September. He is the only physician who has ever been consecrated Pope, and apart from Damasus I (from Roman Lusitania), he has been the only Portuguese pope. Throughout his pontificate, Pope John XXI remained deeply interested in scientific matters. He directed the bishop of Paris, Tempier, to investigate the controversy surrounding the teachings of Aristotle, a directive which resulted in the Parisian bishop issuing  a list of 219 condemned propositions.  The historian and scientist Pierre Duhem believed that Bishop Tempier, with his insistence of God’s absolute power, liberated Christian thought from the dogmatic acceptance of Aristotelianism, and in this way marked the birth of modern science.

Pope John XXI’s maintained strong interest in his personal scientific studies even after his consecration. Indeed, to secure the necessary quiet for his medical studies, he had an apartment added to the papal palace at Viterbo, to which he could retire when he wished to work undisturbed. On 14 May 1277, while the pope was working in this laboratory, it collapsed; John was buried under the ruins and died on 20 May in consequence of the serious injuries he had received. He was buried in the Duomo di Viterbo, where his tomb can still be seen.