The Treaty of Venice was a contract, entered into by Doge Enrico Dandolo and the Venetian Republic on one side, and Baldwin IX of Flanders, Thibaud III of Champagne, and Hugh of Saint-Pol on the other, to provide transport for the army of the Fourth Crusade (1202-1204). The treaty, which was confirmed by Pope Innocent III, committed the Venetians to providing sufficient vessels and provisions for 4,500 knights, 4,500 horses, 9,000 squires, 20,000 infantry, and all of their equipment. The vessels were to remain in the service of the crusade for one year, beginning 29 June 1202. The crusaders were to pay the Venetians 85,000 silver marks of Cologne.
The terms of this treaty would ultimately be responsible for the Fourth Crusade’s tragic diversions: only one-third of the projected number of crusaders arrived in Venice, making it impossible to reimburse the Venetians fully for their enormous expenses. The resulting poverty of the army led the crusade first to Zara (mod. Zadar, Croatia) and then to Constantinople (mod. Istanbul, Turkey) in an attempt to secure the funds necessary to meet the terms of the treaty. In August 1203 the newly crowned Emperor Alexios IV Angelos paid the crusaders for their services, thus closing the books on the troubled treaty. Yet by that time the crusade was already entangled in a thicket of Byzantine politics that would later lead to the conquest of Constantinople in April 1204.