The Origin of the Idea of CrusadeThough conditioned by the specific circumstances of eleventh century Europe, the launching of the crusades presupposed a long historical evolution of the idea of Christian knighthood and holy war. Carl Erdmann developed this argument first in 1935 in a book that is still recognised as basic to an understanding of how the crusades came about. This first edition in English includes notes supplementing those of the German text, a foreword discussing