Mongol capital of Karakorum to convert the Tartars. William visited the court of the great khan Möngke in 1254, and observed representatives of several religions there. He engaged in a famous debate set up by Möngke, with representatives of each religion debating (unsuccessfully) which was best. He left in August 1254, bearing Möngke's reply to King Louis. In 1268, Marco Polo's father and uncle returned from China with an invitation from Kublai Khan to the pope, imploring him that a hundred teachers of science and religion be sent to reinforce the Christianity already present in Kublai's empire. However, this came to naught due to the hostility of influential Nestorian Christians within the largely Mongol court. Kublai did request Western assistance to secure Mongol rule over the Chinese Yuan dynasty. In 1289, Pope Nicholas IV sent the Franciscan John of Monte Corvino to China by way of India. Although Kublai had already died by the time John arrived in 1294, the court at Khanbaliq received him graciously and encouraged him to settle there. John was China's first Roman Catholic missionary, and he was significantly successful. He laboured largely in the Mongol tongue, translated the New Testament and Psalms, built a central church, and within a few years (by 1305) could report 6,000 baptized converts. He also established a lay training school of 150 students. Other priests joined him, John was consecrated a bishop, and centers were established in the coastal provinces of Kiangsu (Yangchow), Chekiang (Hangchow) and Fukien (Zaitun). Under John's influence, many Mongols, such as those of the Ongut tribe, changed allegiance from the Eastern Nestorian (Syro-Oriental) Church, to Western Roman Catholicism. Following the death of Monte Corvino, an embassy to the French Pope Benedict XII in Avignon was sent by Toghun Temür in 1336, requesting a new spiritual guide. The pope replied by appointing four ecclesiastics as his legates to the khan's court. In 1338, a total of 50 ecclesiastics were sent by the Pope to Peking, such as John of Marignolli, who arrived in Khanbaliq in 1342, and stayed until 1347, then returning to Avignon in 1353. However, the Mongol-established Yuan dynasty in China was in decline, and in 1368 was overthrown by the Ming dynasty founded by the native Chinese. The last Catholic bishop of Quanzhou, Giacomo da Firenze, was killed by the Chinese in 1362. By 1369 all Christians, whether Roman Catholic or Nestorian (Syriac Orthodox,