After the failure of the Third Crusade, there was little interest in Europe for another crusade against the Muslims. The Fourth Crusade was the last of the major crusades to be directed by the Papacy, before the Popes lost much of their power to the Holy Roman Empire and other secular monarchs. The later crusades were directed by individual monarchs, and even the Fourth quickly fell out of Papal control.
In 1198, Pope Innocent III called for a new Crusade, which was largely ignored among European leaders. The Germans were struggling against Papal power, and England and France were still engaged in warfare against each other. However, 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. Thibaud was elected leader, but he died in 1200 and was replaced by an Italian count, Boniface of Montferrat. Boniface and the other leaders sent envoys to Venice, Genoa, and other city-states to negotiate a contract for transportation to Egypt, the object of their crusade; one of the envoys was the historianGeoffrey of Villehardouin. Genoa was uninterested but Venice agreed to transport 30 000 crusaders, a very ambitious number.
By 1201 the crusader army was collected at Venice, though with far fewer troops than expected. The Venetians, under the aged and possibly blind dogeEnrico Dandolo, would not let the crusaders leave without being paid the full amount agreed to originally, but the crusaders could only pay half, and only by reducing themselves to extreme poverty. The Venetians barricaded them on the island of Lido until they could decide what to do with them.
Dandolo and the Venetians succeeded in turning the crusading movement to their own purposes. Dandolo, who made a very public show of joining the crusade during a ceremony in the church of San Marco di Venezia, had the fleet instead attack the Hungarian port of Zara, a former Venetian possession in Dalmatia (now Zadar in Croatia). The Hungarian king Emeric was Catholic and had himself "taken the cross", meaning he too had agreed to join the crusade. Many of the crusaders were opposed to this, and some, including a force led by the elder Simon de Montfort, refused to participate altogether and returned home. The citizens of Zara made reference to the fact that they were fellow Catholics by hanging banners marked with crosses from their windows and the walls of the city, but nevertheless the city fell after a brief siege. Both the Venetians and the crusaders were immediately excommunicated for this by Innocent III.
Boniface, meanwhile, had left the fleet before it sailed from Venice, and had visited his cousin Philip of Swabia. The reasons for his visit are a matter of debate; he may have realized the Venetians' plans and left to avoid excommunication, or he may have wanted to meet with Alexius Angelus, Philip's brother-in-law and the son of the recently deposed Byzantine emperor Isaac II. Alexius had fled to Philip when his father was overthrown in 1195, but it is unknown whether or not Boniface knew he was at Philip's court. In any case, Alexius offered to pay off the Crusaders' debt to Venice, if they would restore his family to the Byzantine throne, an offer Boniface found difficult to refuse. Boniface may also have had in mind the former land holdings of his brother Conrad of Montferrat, who had married a daughter of emperor Manuel I Comnenus but had been driven out of the empire around 1190. Alexius returned with Boniface to rejoin the fleet at Corfu after it sailed from Zara, and the Venetians, when they learned of Alexius' idea, were particularly pleased with it. They also had been personally offended by the Byzantines in recent years, as thousands of Europeans (including many Venetians) had been killed in riots against their merchant communities in Constantinople in 1182.
The Crusaders were still reluctant to attack fellow Christians, but the clergy convinced them that the Orthodox Byzantines were the next best thing to the Muslims. They had allied with Saladin against the Third Crusade, and had done nothing to aid the Second Crusade; they should be punished for their lack of support. Unfortunately for them, Alexius Angelus had overstated his importance and it was quickly discovered when the crusaders arrived at the walls of Constantinople that the citizens preferred a usurper to an emperor supported by the hated "Latins." The crusaders and Venetians decided to place Alexius on the throne by force, and an amphibious assault was launched on the city in 1203. Unexpectedly, emperor Alexius III panicked and fled, and the citizens of Constantinople reluctantly welcomed Alexius Angelus back into the city. He was crowned emperor as Alexius IV, and his father Isaac II was restored as co-emperor.
The Crusaders and Venetians, incensed at the murder of their supposed patron, attacked the city once more in 1204. Alexius V, who had a much larger army, although it was much more poorly trained, marched his troops outside Constantinople and seemed to prepare for an all-out assault on the crusader force. As the crusaders panicked and armed everyone they could find, including cooks who wore their pots as helmets, Alexius V turned around and marched his army back into the city. It is possible that his foot soldiers were afraid of the western knights, who had defeated them earlier in the year in skirmishes outside the city, but the actual reason for Alexius' refusal to fight is unknown. Although Innocent III had again warned them not to attack, the papal letter was suppressed by the clergy, and the crusaders prepared for their own attack, while the Venetians attacked from the sea; Alexius' army stayed in the city to fight, along with the imperial bodyguard, the Varangians, but Alexius himself fled during the night.
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. Boniface was not elected as the new emperor, although the citizens seemed to consider him as such; the Venetians thought he had too many connections with the former empire because of his brother's land holdings, and instead placed Baldwin of Flanders on the throne. Boniface went on to found the Kingdom of Thessalonica, a vassal state of the new Latin Empire. The Venetians also founded the Duchy of the Archipelago in the Aegean Sea. Meanwhile, Byzantine refugees founded their own successor states, the most notable of these being the Empire of Nicaea under Theodore Lascaris and the Despotate of Epirus.
Edgar McNeal and Robert Lee Wolff, The Fourth Crusade, in A History of the Crusades (edited by Kenneth M. Setton and others), vol. 2, Philadelphia: University of Pennsylvania Press, 1962
Donald M. Nicol, Byzantium and Venice: A Study in Diplomatic and Cultural Relations ISBN 0521428947
Donald E. Queller, The Latin Conquest of Constantinople, New York, London, Sydney, Toronto: John Wiley and Sons, Inc., 1971
Donald E. Queller and Thomas F. Madden, The Fourth Crusade: The Conquest of Constantinople (2nd Edition, 1999) ISBN 0812217136
D. E. Queller and Susan J. Stratton, "A Century of Controversy on the Fourth Crusade", Studies in Medieval and Renaissance History v. 6 (1969): 237-277; reprinted in D. Queller, Medieval Diplomacy and the Fourth Crusade, London: Variorum Reprints, 1980
