In the spring of 1271 three Venetians set out for Acre, the last Christian stronghold in Palestine: Marco Polo, just seventeen, his father, and his uncle. Venetian merchants frequently travelled around the Mediterranean and Black Sea, for Venice's international trade was already highly organised: in addition to trading convoys, Venetians had their own quarters in numerous foreign ports. Extended Venetian merchant families would thus often have several households around the Mediterranean, and with a house in Constantinople the Polos were one such family. Their journey in 1271 would have been banal had they not intended to go much further than Acre, to the Far East, for just two years earlier the two elder Polos had returned from an extended trip, commissioned as ambassadors to the pope by none other than the Great Khan, Kubilai, ruler of the vast Mongol Empire that stretched across Asia to the edges of Europe. The Polos were to spend twenty-four years in Asia. If his own account is to be believed, Marco learned to speak several non-European languages, was employed as an administrator by Kubilai, and visited places virtually unknown to Europeans, notably Cathay (China), Indochina, Sumatra, Java, Ceylon, and India. Several years after his return, in 1298 – again according to his own account – Marco was imprisoned in Genoa following one of its sporadic naval skirmishes with Venice.