Pope John XXI was born in Lisbon between 1210 and 1220. His original name was Pedro Rebuli Julião and he was also referred to as Petrus Hispanus (Peter of Spain). He was the only Portuguese ever to be pope. Strictly speaking he should have been John XX, but because of an error number XX was skipped, so he became John XXI.

After studying medicine in Paris and perhaps also in Montpellier and Salerno, he served as Professor of Medicine and Ophthalmology at the University of Siena (1247 to1252). Returning to Lisbon, he occupied several ecclesiastical positions, became archbishop of Braga, and was physician to Pope Gregory X in 1272. Elected pope himself in 1276, he ruled over a turbulent world marked by the reconquest of Constantinople by Michael Palaeologos (1261) and followed by several attempts to reunite the Eastern and Western branches of Christianity.^1,2

Pope John XXI wrote three famous books.^3,4 The Liber de Oculo (Book on the Eye) was a treatise on ophthalmology based on earlier Greek and Arabic practices. It consisted of 55 chapters: 41 on eye pathology, 14 on therapy. It reviewed the anatomy and physiology of the eye, followed by descriptions of its diseases and medical treatments, “many of which we should even now consider disgusting, and others too curious to be set down here.”² Yet some continued to be used for centuries, such as when Michelangelo had paint splattered on his face and washed it with a concoction of honey, rose water, and milk.⁴

The second book, The Thesaurus Pauperum (Treasury of the Poor) was for the poor but required an understanding of Latin. It was a prescription handbook of home-made simple and cheap remedies. It discussed forty diseases starting from the head down with hair loss, pustules on the head, headache, eye pain, diseases of the ear, and sore throat, down to jaundice, bowel diseases, tenesmus, strangury, penis itch, and swelling of the testicles. It advised how to stimulate coitus, suppress libido, stop heavy menses, and prevent or enable conception.³

His third book, the Tractatus, was on logic. Structured in twelve parts, it became the basic text for freshmen at every university in the Middle Ages. After his election, Pope John continued to study theology, philosophy, and logic, and he was regarded as the most perfect encyclopedist of the Middle Ages, a true intellectual and savant in whom knowledge about medicine, philosophy, and religion coexisted.^3,4

But the term of his pontificate was cut short. In his palace at Viterbo, he had an apartment constructed where he could study, address fine theological questions, inspect the stars, make experiments, and converse with distinguished scientists and theologians.³ Unfortunately, after only eight months, on May 14, 1277, the ceiling of his bedroom collapsed, and although the pope was rescued, he was severely injured. He died within one week,³ remembered as a man of the widest cultural dimensions. His reign was too short to make substantial changes, yet he has been unfairly criticized as being uninvolved and impractical, “causing more damage than benefit and honor to his pontificate.”³ He is buried in Viterbo, yet in the year 2000, the city council of Lisbon had a funeral monument built in his memory.^3,4

Further reading

1. PG Maxwell-Stuart. Chronicle of the Popes. Thames and Hudson LTD, London,1997: 119.
2. John Julius Norwich. Byzantium, Volume 3 (The Decline and Fall). Alfred A. Knopf, New York, 1996: 241.
3. Natale G. De Santo et al. John XXI, the Pope Philosopher and Physician–Scientist of Portuguese Origins Died of Crush Syndrome in 1277. Journal of Religion and Health (2021) 60:1305-17.
4. Andrei Ionut Cucu et al. The Anatomy of Papal Tiara: A Story About Popes. Journal of Religion and Health (2019) 58:1307-27.