c. 1215-1277

Spanish Physician and Pope

Perhaps the most famous of the medieval scientist-popes—men whose contributions to learning were as important as the fact that they held the most powerful throne in Europe—was Sylvester II, or Gerbert (945-1003). Equally noteworthy, however, was John XXI, who for most of his life was known as Peter of Spain. In addition to his Treasury of Medicines for the Poor, Peter wrote a work on optics, along with one of the medieval world's most influential textbooks on logic.

He was born Pedro Julião in Lisbon between 1210 and 1220, and though Portugal by then had established an identity separate from that of its larger neighbor, he would become known as Pedro Hispano, Petrus Hispanus, or Peter of Spain. During the late 1220s and early 1230s, Peter studied at the University of...