Several popes are regarded by historians as illiterate, including:
Pope Zephyrinus (199–217); St. Hippolytus of Rome wrote "Pope Zephyrinus was illiterate" (Hippol. p. 284, ed. Miller).Pope Adrian IV (1154–1159); George Washington Dean writes: "Adrian IV., the only English Pope, had been an illiterate servant in a monastery at Avignon."Pope Celestine V (1294); Sir Maxwell Herbert writes of Celestine V: "On the commemoration day of S. Paul, Celestinus the Fifth was created Pope, who , albeit illiterate, was the priest and confessor of his predecessor."Pope Innocent VI (1352–1362); It was written of Innocent VI that "the new pope was so illiterate that he looked upon Petrarch as a magician, and this disfavor is supposed to have caused the poet's return to Italy.