The success of the First Crusade, and its capture of Jerusalem in 1099, has been conventionally explained by its ideological and political motivation. This book looks at the First Crusade primarily as a military campaign and asks why it was so successful. Modern writing about the crusade has tended to emphasize the moral dimension and the development of the idea of the crusade, but its fate was ultimately decided on the field of battle. This book looks at the nature of war at the end of the eleventh century and the military experience of all the contending parties in order to explain its extraordinary success.