This to the mediæval mind is the outstanding characteristic of Averrhoïsm. It is insolent in the assurance of its denials. In the fourteenth century Averrhoës himself stands as the unique personification of the spirit of unbelief; and as such is bracketed with Antichrist and Mohammed.[111] In this light he figures in the paintings of Orcagna and others. To Gerson he is the most abominable of all enemies of Christianity, to Petrarch a rabid dog ever raging against the Catholic faith.[112] The famous phrase ‘the three impostors,’ which had first been attributed by Gregory IX to Frederick II, and the essential conception of which in book form was destined to be attributed to many others from Boccaccio to Erasmus, Rabelais to Milton, was fathered upon Averrhoës.[113] He had declared—so it was believed—that Moses, Christ and Mohammed were three impostors who had deluded the world; also that of the three religions, Judaism, Christianity, Mohammedanism, the first was a religion for babes, the second a sheer impossibility, the third fit only for hogs. The Eucharist was the impossible feature of Christianity, and Christians were especially hateful because they ate the flesh of the God whom they professed to adore.[114] Perhaps the most interesting fact connected with the story of the Islamic philosophy in Europe is the fact that it helped to familiarize Christendom with some of the features of another religion. It was not, of course, the sole agency to do that; the Crusades played their part. It is significant that many of the mediæval stories and mystery plays have as their central idea apostasy, which as a rule takes the form of conversion to Mohammedanism. Even the religious wars in Palestine did not breed exclusively antagonism to the faith of the infidel, and friendly intercourse with Saracen Spain and academic interest in Islamic philosophy produced a knowledge that was less critical than sympathetic. Such familiarity with the main conceptions of other creeds rendered feasible the comparative study of religion. That was to be an achievement for a future age. Yet it needed no exact science of the subject to encourage the spirit of toleration. When other religions were discussed, were it only for the sake of attacking and refuting them, still the curious eye could not fail to be aware of their common elements. Not even in Marsiglio is the principle of religious toleration more notably set forth than in one of the tales of the ‘Decameron,’ the pithy parable of ‘The Three Rings,’ which inspired Lessing’s ‘Nathan the Wise.’[115] Melchizedek in Boccaccio’s tale emphasizes in his analogue the common elements in the three religions of Jew, Moslem and Christian, each claiming to be the sole truth, and no doubt one of them being in fact the truth, yet so alike that none can tell which that one is. Boccaccio’s attitude is one of sceptical indifference, and it is no far cry from that to the attitude of Pulci