Lower, Michael. The Barons' Crusade: A Call to Arms and Its Consequences

University of Pennsylvania Press, 2005. - 272 p. - The Middle Ages SeriesIn 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 last until 1241 and would represent in many ways the high point of papal efforts to make crusading a universal Christian undertaking. This book, the first full-length treatment of the Barons' Crusade, examines the call for holy war and its consequences in Hungary, France, England, Constantinople, and the Holy Land.