[731] In the reign of the latter monarch the Mongols in China began to yield to the powerful influences of the surrounding Buddhism, and by the beginning of the fourteenth century the Buddhist faith seems to have gained a complete ascendancy over them. [732] It was the Lamas of Tibet who showed themselves most zealous in this work of conversion, and the people of Mongolia to the present day cling to the same faith, as do the Kalmuks who migrated to Russia in the seventeenth century. Although Buddhism made itself finally supreme in the eastern part of the empire, at first the influence of the Christian Church was by no means inconsiderable and great hopes were entertained of the conversion of the Mongols. The Nestorian missionaries in the seventh century had carried the knowledge of the Christian faith from west to east across Asia as far as the north of China, and scattered communities were still to be found in the thirteenth century. The famous Prester John, around whose name cluster so many legends of the Middle Ages, is supposed to have been the chief of the Karaïts, a Christian Tartar tribe living to the south of Lake Baikal. When this tribe was conquered by Chingīz Khān, he married one of the daughters of the then chief of the tribe, while his son Ogotāy took a wife from the same family. Ogotāy’s son, Kuyūk, although he did not himself become a Christian, showed great favour towards this faith, to which his chief minister and one of his secretaries belonged. The Nestorian priests were held in high favour at his court and he received an embassy from Pope Innocent IV. [733] The Christian powers both of the East and the West looked to the Mongols to assist them in their wars against the Musalmans. It was Hayton, the Christian King of Armenia, who was mainly instrumental in persuading Mangū Khān to despatch the expedition that sacked Baghdād under the leadership of Hūlāgū, [734] the influence of whose Christian wife led him to show much favour to the Christians, and especially to the Nestorians. Many of the Mongols who occupied the countries of Armenia and Georgia were converted by the Christians of these countries and received baptism. [735] The marvellous tales of the greatness and magnificence of Prester John, that fired the imagination of mediæval Europe, had given rise to a belief that the Mongols were Christians—a belief which was further strengthened by the false reports that reached Europe of the conversion of various Mongol princes and their zeal for the Christian cause. It was under this delusion that St. Louis sent an ambassador, William of Rubruck, to exhort the great Khāqān to persevere in his supposed efforts for the spread of the Christian faith. But these reports were soon discovered to be without any foundation in fact, though William of Rubruck found that the Christian religion was freely tolerated at the court of Mangū Khān, and the adhesion of some few Mongols to this faith made the Christian priests hopeful of still