The Fourth Crusade and the Long Thirteenth Century: From Constantinople to the Fall of Acre

The Fourth Crusade was called by Pope Innocent III in 1198 with the aim of attacking Egypt, seen as the strategic center of Ayyubid power. Its leaders contracted the Republic of Venice, under Doge Enrico Dandolo, to provide naval transport in exchange for a large payment; when the expected number of crusaders and the money to pay Venice both fell short, Venice demanded as compensation an attack on the Christian city of Zara in Dalmatia in 1202, which led Pope Innocent III to temporarily excommunicate the crusaders. The Byzantine prince Alexios Angelos then asked the crusaders for help restoring his deposed father Isaac II to the throne, offering money, troops, and the union of the Churches in return; the crusaders diverted the expedition to Constantinople, restored Isaac II and Alexios IV in 1203, and when Alexios IV failed to deliver on his promises a coup brought Alexios V Doukas to the throne instead. With their financial expectations dashed, the crusaders attacked and conquered Constantinople itself in April 1204, subjecting the city to a brutal sack and installing Baldwin of Flanders as the first Latin emperor of Constantinople — an episode that deepened, almost irreversibly, the schism between the Catholic and Orthodox Churches.