1. Name and nature of the movement. Since the 18th century the term “Crusades” (medieval Latin cruciata, 13th century) has been applied to all the armed pilgrimages and military expeditions, sponsored by the medieval Church, that were undertaken against unbelievers and heretics by the crucesignati — people who had taken vows and wore a cloth cross sewn on their garments.

The idea of the crusade, a special form of the idea of the just and holy war, looms large in the history of Western piety and thought, casting its shadow beyond the age of the Crusades p…