Though the attempt has been made to identify the Christian potentate of the legend with a chieftain of the Caucasus,[1328] the weight of evidence would seem to favor belief that the story in its more specific thirteenth-century form grew out of rumors of some Christian Mongol lord of Central Asia.[1329] It is certain that the Nestorian form of Christianity was strongly represented in Central Asia during this period and that two powerful tribes of these distant regions, the Keraïts and the Onguts, formed outposts of this faith. But, as Pelliot writes, “whatever may have been the origin of the famous legend of Prester John, ... it was to a prince of the Keraïts that the tradition was applied during the first half of the thirteenth century. All the Keraïts spoken of in the history of the Mongol dynasty seem to have been Christians; in any case this is true of the majority of them. In fact it was through marriage with Keraït princesses that Christianity penetrated even into the family of Jenghiz Khan.”[1330] Many of these Asiatic Christians bore Christian names preserved in Chinese forms, such as Yao-su-mu for Joseph or K’wo-li-ki-ssö for George.[1331] We learn from Marco Polo and other thirteenth-century travelers that Mongol princes often submitted to baptism, though this was probably done out of indifference to religion rather than as the expression of any deep-seated convictions. On such slender foundations as the report in Otto’s _Chronicon_ or the anonymous account of the visit of the Patriarch John to Rome or on other rumors of events in the heart of Asia of which no record has been preserved, there was erected an elaborate, detailed, and wholly fanciful series of descriptions of Prester John and his realm, embellished by borrowings from the Romance of Alexander, from the legend of St. Thomas, and from that world of fable which constituted the medieval European conception of the Orient. _Prester John’s Kingdom As Described in His “Letter”_