If in the Middle Ages these various attitudes of mind were not fully distinguished, yet scepticism was moving variably towards the demand for verification on which all natural science is based; and the reaction was not long delayed. In the thirteenth century the culture of Omeyad and Abasid caliphs failed; by the end of the century philosophy was denounced and its books were burned; the generous and learned Frederick dashed himself in vain against the Papacy; Clement, the protector of Bacon, was dead, and during the two following centuries, in Spain at any rate, freedom of thought was crushed out by the Church. In the fourteenth and fifteenth centuries the very name of Averroes—of “the mad dog who barked against the Christ,” the “Averroem impium καὶ τρὶς κατάρατον” of Erasmus—began to signify loose life as well as free thought. Of this resentment there had been no trace in Albert or St Thomas; but Imola had begun to wonder why Dante had treated so well Averroes who, if the Great Commentator, was yet the father of infidels. The Dominicans controlled the fine arts, and for them,—at Pisa, at Siena, in the Spanish Chapel,—Orcagna, Gaddi, Spinello Aretino, Simone Memmi abased the Empire, Averroes, and the new learning far more intolerantly than Dante had done; and exalted the Pope, with his handmaids Theology, Grammar, Logic, and Rhetoric. In Santa Maria Novella, Memmi represents the triumph of the Dominicans in theology, Gaddi in philosophy; St Thomas and the Dominicans march triumphant over Arius, Sabellius, Averroes, and Savonarola. Thus in the Middle Ages Averroes appeared in two forms—first as the Great Commentator, later as the blasphemer and father of infidels of the Campo Santo and of Santa Maria Novella. In the fifteenth century the Council of Constance forbad the laity to teach, under a penalty of forty days’ excommunication. In the sixteenth, in Granada, Ximenes burnt, it is said, 80,000 books of Arab philosophy, as Torquemada did for Hebrew in Seville; medical works, however, such as the Colliget[60] of Averroes, and his Commentary on Galen, were spared.