In 1095, Pope Urban II called for Christian warriors to ‘liberate’ Jerusalem from Muslim rule. Four years later, against extraordinary odds, they succeeded. It seemed miraculous, and the attempt to hold or reconquer the resulting Christian principalities would echo down the centuries. Even after the idea of a military crusade faded from favour, the word remained synonymous with militant and focused campaigning. With 9/11 and the emerging perception of the Islamic world as the new, post-Communist “favoured enemy” of the West, the crusade’s meaning as an expression of religious violence returned with force. But what did it mean to go on crusade in the Middle Ages, especially in its heyday? And what does it mean now? Is a “clash of civilizations” (Samuel P. Huntington) inevitable or a phantasm conjured by misunderstanding the Middle Ages?