The Barons' CrusadeIn December 1235, Pope Gregory IX altered the mission of a crusade he had begun to preach the year before. Instead of calling for Christian magnates to go on to fight the infidel in Jerusalem, he now urged them to combat the spread of Christian heresy in Latin Greece and to defend the Latin empire of Constantinople. The Barons' Crusade, as it was named by a fourteenth century chronicler impressed by the great number of barons who participated, would