Why Did the Fourth Crusade Sack Constantinople?
The Fourth Crusade sacked Constantinople in April 1204 for a combination of reasons: the Crusaders’ debt to Venice, the political crisis in the Byzantine Empire, the role of Enrico Dandolo, and the personal ambitions of the Crusade’s leaders. The standard English-language account is Jonathan Phillips’s The Fourth Crusade and the Sack of Constantinople (2004), with the older Thomas Madden and Donald Queller monographs providing essential background. The result was one of the most controversial events in medieval history: the capture and three-day pillage of the largest Christian city in the world, the establishment of the Latin Empire of Constantinople, and a fatal weakening of the Byzantine Empire that would last until 1453. The question of whether the diversion was a Venetian plot, an accident, or a sequence of contingent decisions is the central historiographical question, and the answer depends on how one defines each of those terms.
For the broader context, see the main article on the Fourth Crusade, the Sack of Constantinople (1204), and the role of Venice.
The Financial Trap
The most immediate reason for the sack of Constantinople was the financial situation of the Crusade. The army had contracted with Venice in 1201 to provide ships and provisions for the expedition to the Holy Land. The cost was 85,000 silver marks, a sum the Crusaders were unable to raise in full. By the time the army gathered in Venice in 1202, the Crusaders had paid only about half of the sum owed.
The Venetian response was to offer a deal: the Crusaders could pay off their debt by helping Venice to capture the Adriatic port of Zara, which had recently rebelled against Venetian rule. The attack on Zara, a Christian city, was a violation of papal orders, and Pope Innocent III excommunicated the entire army. The capture of Zara in November 1202 worsened the financial situation, because the army now had to pay off the additional obligations.
The financial trap was now serious. The Crusaders owed Venice even more than before, and they had no way to pay off the debt except through further military action. The opportunity came with the arrival in the Crusader camp of Alexios, the son of the deposed Byzantine Emperor Isaac II Angelos. Alexios offered the Crusaders a substantial sum of money, military support, and the union of the Greek and Latin churches, in return for their help in restoring his father to the throne.
The Byzantine Political Crisis
The Byzantine Empire in 1203 was in the midst of a succession crisis. The emperor Isaac II Angelos had been deposed, blinded, and imprisoned by his brother Alexios III. Isaac’s son, Alexios the Younger, escaped from Constantinople and made his way to the Crusader camp. The young prince’s offer was tempting: substantial sums of money, military support, and the union of the Greek and Latin churches.
The decision to accept Alexios’s offer was made by the leadership of the expedition, with Enrico Dandolo playing a central role. The Crusader army sailed to Constantinople in April 1203, and the first siege of the city, in July 1203, was a success. Isaac was restored to the throne, and Alexios IV was co-emperor. But the new regime was unable to fulfill its promises, and in January 1204, a palace coup overthrew Isaac and Alexios IV. The new emperor, Alexios V, refused to honor the agreement with the Crusaders.
The political crisis in the Byzantine Empire was therefore the direct cause of the sack. Without Alexios’s offer, the Crusaders would not have gone to Constantinople. Without the palace coup of January 1204, the Crusaders would not have attacked the city. The Byzantines themselves created the conditions for the sack of 1204.
The Role of Enrico Dandolo
The role of the Doge of Venice, Enrico Dandolo, in the diversion of the Fourth Crusade has been the subject of intense historical debate. Older historians portrayed Dandolo as a cynical Venetian merchant who deliberately diverted the Crusade to advance Venetian commercial interests. More recent scholarship, especially that of Thomas Madden and Jonathan Phillips, has emphasized the complex political and commercial context in which Dandolo acted.
There is no doubt that Dandolo was the principal architect of the diversion. He negotiated the original contract with the Crusaders, he made the deal at Zara, and he led the assault on Constantinople. He was an elderly, nearly blind man, but he was a brilliant statesman, and he shaped the entire expedition. Whether he was acting in the legitimate interests of Venice, or whether he was pursuing a personal vendetta against the Byzantines, is a matter of historical debate.
The relationship between Dandolo and the Byzantine Empire was also shaped by the legendary story of his blinding. According to the version preserved by the chronicler Geoffrey of Villehardouin, Dandolo had been blinded by the Byzantines during an earlier diplomatic mission. The story is probably false, but it became a powerful explanation for Dandolo’s hostility to the Byzantine Empire.
The Failure of the Union
The most important reason for the sack, in the eyes of many contemporaries, was the failure of the union of the Greek and Latin churches. The union had been a long-standing goal of the papacy, and the bull Quia maior of Innocent III, calling the Fourth Crusade, had emphasized the importance of bringing the Greek Church back into communion with Rome. The failure of the union in 1204, when the Greek population of Constantinople rejected the agreement, was a major blow to the papal agenda.
The failure of the union was a result of deep-seated cultural and religious differences between the Latin West and the Greek East. The Greek Orthodox Church had its own traditions, its own theological positions, and its own political interests. The Latin Church’s attempt to impose union was perceived by many Greeks as an act of aggression. The result was a deep and lasting split between the two churches, a split that would not be healed until modern times.
The sack of Constantinople, in this sense, can be seen as the failure of a long effort to bring the two churches together. The Latin Church had tried persuasion, negotiation, and ultimately force, and the result was the deepest schism in Christian history.
The Personal Ambitions of the Leaders
The personal ambitions of the leaders of the Fourth Crusade also played a role. The most important of these was the Marquis Boniface of Montferrat, who had long claimed the throne of Constantinople. The decision to attack Constantinople was supported by Boniface and by the other great nobles of the expedition, who saw the opportunity to win new principalities and titles.
The role of Enrico Dandolo in these personal ambitions is also significant. The doge was the most powerful figure in the expedition, and he had his own agenda. The diversion of the Crusade to Constantinople served Venetian commercial interests, and it also gave Dandolo a prominent place in the politics of the Eastern Mediterranean. The death of Dandolo in 1205, just a year after the sack, removed a major figure from the politics of the new Latin Empire.
The Long-Term Consequences
The sack of Constantinople had long-term consequences for the medieval world. The Byzantine Empire was fatally weakened, and it would not fully recover before the Ottoman conquest in 1453. The Greek Orthodox Church was split from Rome in a way that would last for centuries. The cultural treasures of Byzantium were dispersed across Europe, and the Latin West gained access to the wealth of Greek learning that would eventually fuel the Renaissance.
The sack also had consequences for the Crusading movement. The diversion of the Fourth Crusade was a major moral failure, and it showed the limits of the papacy’s control of the Crusading movement. The Fifth Crusade and subsequent expeditions would be conducted with greater care, but the memory of 1204 would linger. The Latin Empire, meanwhile, would divert Western resources from the defense of the Latin East, making the Crusader States more vulnerable to Muslim pressure.