The Polos were among the most prominent Genoese and Venetian merchants who operated between the Black Sea and Persia in the thirteenth century. Following the Silk Road, Marco Polo's (1254-1324) father and uncle reached modern-day Beijing, glorious capital of a vast territory dominated for approximately a century by the dynasty of the Great Khan Kublai (1215-1294), grandson of Genghiz Khan (1167?-1227). Kublai asked the Polos to serve as ambassadors to the Pope, conveying a request to send a mission to the Mongol court that would bring preachers and physical evidence of the Christian world. The Polos returned to Venice but soon journeyed back to the Great Khan's court. They took with them the young Marco, who may have spoken Persian, one of the languages of the Mongol-Chinese bureaucracy. This enabled Marco Polo to visit many cities of the empire as a court functionary. The travel accounts recorded in Marco Polo's celebrated Book of the Marvels of the World (Il Milione) were written after his return to Venice, probably during his imprisonment in Genoa in 1298, and in collaboration with the poet Rustichello da Pisa (2nd half of 13th cent.). Their book was published in manuscript around 1300 and enjoyed a very wide circulation in several languages. It offered the outline of a comprehensive economic and political geography of Asia, described as a dense network of overland, river, and maritime trade routes. By following these routes, the Mediterranean region and Christian Europe were linked with the remotest parts of Asia. The world's boundaries now stretched eastward to the immensely rich island kingdom of Cipangu, modern-day Japan, which Marco Polo's book described for the first time.