The Mongol Empire's rise gave Western Christians the opportunity to visit lands that they had never seen before, and they set out in large numbers along the empire's secure roads. Belief that a lost Nestorian kingdom existed in the east, or that the Crusader states' salvation depended on an alliance with an Eastern monarch, was one reason for the numerous Christian ambassadors and missionaries sent to the Mongols. These include Franciscan explorers Giovanni da Pian del Carpine in 1245 and William of Rubruck in 1253.