Pope from 1276. Peter of Spain was born in Lisbon, probably not later than c.1205. In 1273 he was elected Abp. of Braga and created Cardinal Bishop of Frascati; in this capacity he attended the Second Council of Lyons (1274). As Pope he was concerned to preserve the union with the Greek Church achieved at Lyons, and in 1277 he required the Bp. of Paris to report to him those who were teaching errors prejudicial to the faith.
Peter of Spain's Tractatus or Summulae logicales was probably composed in N. Spain in the early 1230s; it is the most influential medieval manual on logic. (The identity of the author of the Tractatus and the future Pope has been challenged, but is generally accepted.) He also wrote other works on logic and medicine and was among the first to comment on various works of Aristotle.