Fourth Crusade

As there was no binding agreement among the crusaders that all should sail from Venice, many chose to sail from other ports, particularly Flanders, Marseilles, and Genoa. By 1201 the bulk of the crusader army was collected at Venice, though with far fewer troops than expected; 12,000 out of 33,500. Venice had performed her part of the agreement: there lay 50 war galleys, 150 large transports, and 300 horse transports - enough for three times the assembled army. The Venetians, under their aged and blind Doge, would not let the crusaders leave without paying the full amount agreed to, originally 85,000 silver marks. The crusaders could only pay some 51,000 silver marks, and that only by reducing themselves to extreme poverty. This was disastrous to the Venetians, who had halted their commerce for a great length of time to prepare this expedition.

Dandolo and the Venetians succeeded in turning the crusading movement to their own purposes as a form of repayment. Following the 1182 massacres of all foreigners in Constantinople, the Venetian merchant population had been expelled by the ruling Angelus dynasty with the support of the Greek population. These events gave the Venetians a hostile attitude towards Byzantium. Dandolo, who joined the crusade during a public ceremony in the church of San Marco di Venezia, proposed that the crusaders pay their debts by attacking the port of Zara in Dalmatia. The city had been dominated economically by Venice throughout the twelfth century, but had rebelled in 1181 and allied with King Emeric of Hungary and Croatia (the two were in a personal union). Subsequent Venetian attacks were repulsed, and by 1202 the city was economically independent, under the protection of the King.

The Hungarian king was Catholic and had himself agreed to join this Crusade (though this was mostly for political reasons, and he had made no actual preparations to leave). Many of the Crusaders were opposed to attacking Zara, and some, including a force led by the elder Simon de Montfort, refused to participate altogether and returned home. While the Papal Representative to the Crusade Peter Cardinal Capuano endorsed the move as necessary to prevent the crusade's complete failure, Pope Innocent was alarmed at this development and wrote a letter to the Crusading leadership threatening excommunication.

Historian Geoffrey Hindley's The Crusades: Islam and Christianity in the Struggle for World Supremacy mentions that in 1202, Innocent III “forbade” the Crusaders of Western Christendom from committing any atrocious acts on their Christian neighbours, despite wanting to secure papal authority over Byzantium (Hindley 143, 152). This letter was concealed from the bulk of the army and the attack proceeded. 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 threatened with excommunication for this by Innocent III.