At Moson, the river Danube ran red with blood. At Antioch, the Crusaders -- their saddles freshly decorated with sawed-off heads -- indiscriminately clogged the streets with the bodies of eastern Christians and Turks. At Ma'arra, they cooked children on spits and ate them. By the time the Crusaders reached Jerusalem, their quest -- and their violence -- had become distinctly otherworldly: blood literally ran shin-deep through the streets as the Crusaders overran the sacred city.

Beginning in 1095 and culminating four bloody years later, the First Crusade represented a new kind of warfare: holy, unrestrained, and apocalyptic. In Armies of Heaven, medieval historian Jay Rubenstein tells the story of this cataclysmic event through the eyes of those who witnessed it, emphasizing the fundamental role that apocalyptic thought played in motivating the Crusaders. A thrilling work of military and religious history, Armies of Heaven will revolutionize our understanding of the Crusades.