Roger Bacon (1214-1294) was an English philosopher and Franciscan friar who placed considerable emphasis on the study of nature through empirical methods. He became a master at Oxford, lecturing on Aristotle. Between 1237 and 1245, he began lecturing at the University of Paris. In 1256 he became a friar in the Franciscan Order, and no longer held a teaching post. After 1260, his activities were restricted by a Franciscan statute prohibiting friars from publishing books or pamphlets without prior approval. He circumvented this through his acquaintance with Cardinal Guy le Gros de Foulques, who became Pope Clement IV in 1265. Clement IV issued a mandate ordering Bacon to write to him concerning the place of philosophy within theology. Bacon sent the Pope his Opus Majus. Some time between 1277 and 1279, Bacon was imprisoned or placed under house arrest for his excessive credulity in alchemy and for his harsh regard for the other innovators of his time. He is believed to have died in 1294.