Fourth CrusadeThe Fourth Crusade (1202-1204), instead of attacking Muslims, conquered the Christian Byzantine Empire of Constantinople in 1204.
After the third crusade, the vital crusading spirit was dead, and the succeeding crusades are to be explained rather as arising from the efforts of the papacy in its struggle against the secular power, to divert the military energies of the European nations toward Syria.
In 1198, Pope Innocent III called for a new Crusade, which was largely ignored among European leaders. Due to the preaching of Fulk of Neuilly, a Crusading army was finally organized at a tournament held at Ecry by Count Thibaud of Champagne in 1199. By 1201 this army was collected at Venice under the leadership of Boniface of Montferrat, with arrangements for the Venetians to transport them to Egypt. The Venetians, under their astute doge, Enrico Dandolo, succeeded in turning the crusading movement to their own purposes. As the Crusaders numbered far fewer than originally expected, they could not pay the Venetians for transport. Dandolo had the fleet instead attack the Hungarian port of Zara, a former Venetian possession. The King of Hungary was a Catholic and had himself "taken the cross", which means that he had agreed to become a crusader. The citizens of Zara made reference to this fact and their own Catholicism by hanging banners marked with crosses from their windows and the walls of the city, but the crusaders were unmoved and the city fell. The Venetians were immediately excommunicated for this by Innocent III.
At Zara, Boniface rejoined the fleet after his visit with his cousin Philip of Swabia, where he had also met with Alexius Angelus, the son of the deposed Byzantine emporor Isaac II, and brother-in-law of Philip. Alexius offered to pay off the Crusaders' debt to Venice if they would restore his family to the Byzantine throne. The Venetians were also open to this idea, as they had recently been offended by the popular riots against their merchant communities in Constantinople.
The Crusaders threw themselves against the Byzantines. Alexius Angelus had overstated his importance and it was quickly discovered that the citizens preferred a usurper to an emperor supported by the "Latins." An amphibious assault was launched on the walls of Constantinople in 1203. Emperor Alexius III panicked and fled, to be replaced by Alexius Angelus, now Alexius IV, and his father Isaac II restored as co-emperor.
Alexius rescinded on his bargain when he realized the imperial treasury was unable to repay the Venetians. Alexius also had to deal with the intense hatred by the citizens of Constantinople for the "Latins" in their midst. One of his courtiers, Alexius Ducas Murtzuphlos, soon overthrew him and had him strangled to death. Alexius Ducas took the throne himself as Alexius V.
The Crusaders and Venetians, incensed at the murder of their supposed patron, attacked the city once more in 1204. Alexius V was no match for an army of western knights, and fled the city in the middle of the night. The victorious Crusaders inflicted a horrible and savage sacking on Constantinople for three days, during which many ancient works of art were stolen or destroyed. Finally, according to a pre-arranged treaty, the empire was apportioned between Venice and the Crusade's leaders and the Latin Empire at Constantinople was established.