The Hohenstaufen emperor Frederick II. then sent for Aristotelian books from Constantinople and had them translated into Latin. At first, indeed, on the first appearance of the Aristotelian writings, the Church made difficulties; the reading of his metaphysics and physics and the abstracts prepared therefrom, as also the exposition of the same, was forbidden by a church synod held at Paris 1209. Likewise in 1215 the cardinal Robert Corceo came to Paris and there held a visitation of the university, on which occasion he ordained that regular lectures on the dialectical writings of Aristotle should be held while he forbade the reading of and lecturing on the metaphysics and natural philosophy of Aristotle, and the abstracts prepared from them; he also condemned the doctrines of the heretics David of Dinant and Amalrich and likewise the Spaniard Mauritius. Pope Gregory, in a bull issued to the University of Paris in 1231, without mentioning metaphysics, forbade the books of the Physics to be read until they had been examined and purified from all suspicion of error. But later on, in 1366, it was on the other hand ordained by two cardinals that no one could be made a _magister_ unless he had studied the prescribed books of Aristotle—amongst which were the Metaphysics and some of the Physics—and had proved himself capable of explaining them.[33] It was only much later on, however, when Greek literature in general had again become widely diffused, that men became better acquainted with the Greek text of the Aristotelian writings. b. ALBERTUS MAGNUS.