William of Rubruck
In 1253, King Louis IX sent the Franciscan William of Rubruck to the 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.