Hagiographical literature has long been acknowledged by historians of medieval West as an important source for understanding past. (1) Yet its potential--and this is especially true in case of medieval Russian sources--remains little explored by historians of Eurasia. (2) Russian sources, with their largely parochial outlook and infrequent references to outside world, cannot compete with eloquence of contemporary Persian chroniclers or with meticulousness of Chinese imperial scribes. (3) In this respect, Tale of Venerable Peter, Prince from Horde (Povest' o Blazhennom Petre, tsareviche ordynskom)--a 15th-century vita that describes conversion of a Mongol prince to Christianity, his move to Russian principality of Rostov, and building of a church there--constitutes an exceptional source. The ritual that consecrated land and church betrays, in my opinion, existence of a Mongol layer buried within medieval Russian hagiographical text. It thereby offers a unique glimpse not only of Mongol religious practices but also of process of conversion and converging religious beliefs. At core of tale lies a legal dispute over fishing rights in Lake Nero between ruling (Riurikid) family of Rostov and descendants of a Mongol whom we know only by his Christian name, Peter. (4) According to text, Peter was a Mongol prince (porody khanska) who happened to witness miraculous healing of his relative by Kirill, bishop of Rostov (d. 1262), while latter was visiting Golden Horde. Impressed by power of Christian prayer, Peter began to question Mongol worship of the sun, moon, stars, and fire and followed Kirill to Rostov. (5) There, after seeing church adorned with gold and pearls and hearing liturgy, young Mongol decided to convert to Christianity. Kirill, afraid to provoke anger of Horde, cautiously waited; and only after Berke Khan's death (1267), which was later followed by civil war within Golden Horde, did he finally agree to baptize his protege. Some time passed; and one day, while hunting, Mongol prince fell asleep and had a vision of apostles Peter and Paul ordering him to build a church on this spot. He petitioned prince (kniaz') of Rostov to sell him plot of land where vision had occurred. The Russian prince, at first suspicious of Peter's intentions (mostly due to latter's Mongol background), eventually agreed and later even befriended young Mongol and granted him many lands from his patrimony (votchina). The two princes eventually became sworn brothers; and Peter, after permanently settling in Rostov and marrying a girl from Rostov's Tatar (i.e., Mongol) quarter, lived a long and happy life. (6) He also founded a monastery, adjacent to church he had built years earlier, to which he retired after death of his wife. The Tale then continues to describe a legal dispute between grandchildren of two princes about ownership of lake next to Peter's monastery. The Russian side claimed that although their grandfather had sold land to his sworn brother, lake had not been mentioned in agreement. Therefore, lake belonged to them. Peter's grandchildren appealed directly to Horde, evoking their Chinggisid ancestry and their relationship to Horde's ruler, whom they addressed as uncle. The khan sent an ambassador to investigate matter, and it was settled in favor of Peter's family. The same issue arose in next generation, however, and entire process was repeated, with Peter's descendants gaining upper hand once again. The text ends with Ignat, Peter's great-grandson, who saved city of Rostov from destruction at hands of a Mongol raiding expedition. Coming out before Mongol troops and again invoking his Mongol blood, Ignat explained that since his great-grandfather had bought land from prince of Rostov, it now belonged to his descendants and therefore to Horde. …