The Fourth Crusade (1202-4) was proclaimed by Innocent IV with the aim of recovering the Holy Places in Palestine. However, the Crusade was financed by the Venetians and at once was diverted to their own ends. In April 1204 this led to the sack of Constantinople, the greatest city in Christendom, and the establishment of a Latin Empire there for the next few decades. This enormously significant event, which destroyed any remaining credibility in the whole Crusading enterprise, is still a mystery to many in the West. This account is an attempt to understand the apocalyptic events of 1204, to explAin how and why they happened, and to examine the context in which they occurred. It is the story of how an army that went forth in the name of God lost sight of its fundamental motivations and how a misguided idealism can often lead to disaster.