During his stay among the Mongols in May of 1254, the Franciscan friar William of Rubruck took part in a debate at the Mongol court. The khan, Baatu, promoted a formal theological debate between the Christians, the Buddhists, and the Muslims. The purpose of the debate was to determine which faith was correct, as decided by three judges. In this portion of his report, presented in the form of a long letter to King Louis IX of France, William relied on biblical passages and orthodox Christian doctrine to assert the validity of Christian claims to being the one true religion.