There is a vigorous debate on the exact beginnings of the Crusades, as well as a growing conviction that some practices of crusading may have been in existence, at least in part, long before they were identified as such. The Prehistory of the Crusades explores how the Crusades came to be seen as the use of aggressive warfare to Christianise pagan lands and peoples. Reynolds focuses on the Baltic, or Northern, Crusades, an aspect of the Crusades that has been little documented, thus bringing a new perspective to their historical and ideological origins.

Baltic Crusades were distinctive because they were not directed at the Holy Land, and they were not against Muslim opponents, but rather against pagan peoples. From the Emperor Charlemagne's wars against the Saxons in the 8th and 9th centuries to the Baltic Crusades of the 12th century, this book explores the sanctification of war in creating the ideal of crusade. In so doing, it shows how crusading ultimately developed in the 12th and 13th centuries. The Prehistory of the Crusades provides a valuable insight into the topic for students of medieval history and the Crusades.