The very possibility of the existence of such a comparison presupposes intercourse with disciples of foreign creeds. The Christians now no longer possessed a merely vague knowledge of Jews and Mahometans. The crusades were expiring, the danger which evoked them had subsided, and the enmity which supported them was decaying. Europe had entered into relations of commerce, if not of amity, with Mahometan nations; and through contact with them had come to measure them by an altered standard, and to acquire the idea of comparing religions. Frederick II, to whom this expression is imputed, is stated to have manifested admiration of Mahometan literature, and affection for his Mahometan subjects who afforded him aid in carrying out the plans of civilization which his powerful mind had formed;(291) and it was his indifference to a crusade, induced probably by other causes, which led the Pope to impute to him the blasphemy just quoted. The contact with the East, half a century later, in like manner afforded the pretext for fastening a charge of unbelief on the Knights Templars.(292) Contact with Mahometans had thus, we have reason to believe, created a latitude of thought in many parts of Christendom. The same idea of the comparison of Christianity with other creeds reappears in a tale of Boccaccio,(293) in which the three great religions are represented under the allegory of three rings which a father gave to his children, so exactly alike that the judges could not decide which was the genuine one of the three, and which the copies. It is also illustrated by the tradition of the existence of a book, entitled “De Tribus Impostoribus,” which has been attributed almost to every great name in the middle ages which was conspicuous for opposition to the claims of the church, or for uneasiness under the pressure of its dogmatic teaching. The existence of the book is legendary: no one ever saw it: and the two distinct works which now bear the title can be shown to have been composed respectively in the sixteenth and seventeenth centuries: but the legend is a witness to the fact of the existence of the idea which the book was said to embody. (20)