Book excerpt: A fascinating, illustrated account of the betrayal of Byzantium, the clash of Western and Eastern Christian factions and the sacking of Constantinople. The Fourth Crusade was the first, and most famous of the 'diverted' Crusades, which saw the Crusade diverted from its original target, Ayyubi Egypt, to attack the Christian city of Zadar in modern Croatia instead, an attack that was little more than a mercenary action to repay the Venetians for their provision of a fleet to the Crusaders. This book examines the combined action and sacking of the city of Zara, which saw the Crusaders temporarily excommunicated by the Pope. It features detailed accounts of the diverse military action, which involved large-scale sieges, amphibious battles and landings and a combined action as the Crusaders fought side-by-side with Venetian troops. Alongside battlescene maps and illustrations, David Nicolle evaluates how the influence of the Venetians prompted an attack on Constantinople, analyses the siege that followed and describes the naval assault and sacking of the city which saw the Crusaders place Count Baldwin of Flanders on the Byzantine throne.