In 1202, six French envoys of the Fourth Crusade (1202-1204) arrived in Venice in hopes of acquiring a fleet and supplies. After the initial agreements fell through and when more crusaders arrived in Venice in June 1202, Doge Enrico Dandolo signed a treaty with the leaders of the Fourth Crusade who, in return for the fifty fully armed galleys and knights, agreed to support the Venetians to capture Zadar, a city that accepted the King of Hungary and Croatia’s suzerainty in 1186. Although the crusaders had an agreement with the Venetian Doge Enrico Dandolo for transport across the sea, the price far exceeded what they were able to pay. In order to reach an agreement Venice set the condition that the crusaders help them capture Zadar, Trst (Trieste), Muggia and Pula. In addition, Doge Enrico Dandolo proposed that the Crusaders agree to remain in Zadar during the winter after the city’s capture in order to reduce the threat of pirates attacks on Venetian commerce and to support Venetian’s interest in regaining military and commercial control in Dalmatia. Additionally, the plan to capture Zadar helped convince the Great Council of Venice to consent to the Doge’s plan. With the enthusiastic support of the Venetians and the Great Council, the Republic of Venice’s participation in the Fourth Crusade was confirmed.
The siege of Zadar was the first major action of the Fourth Crusade and the first attack against a Catholic city by a Catholic Crusader army. The large Crusader army and armada arrived at Zadar in November 1202. At the commencement of the siege, Doge Enrico Dandolo gave the citizens of Zadar an ultimatum – to either leave the city immediately or remain an be killed. Confusion ensued, as Pope Innocent III forbade the Crusade from participating in a siege of a Catholic city and in actions unrelated to their original religious agenda, especially since Zadar was under the suzerainty of King Emerik of Hungary who had himself participated in a crusade in the name of the Pope.
Although a part of the Crusaders refused to take part in the siege and returned home, the attack on Zadar began on 11th November 1202 despite letters from Pope Innocent III forbidding such an action and threatening excommunication. Zadar fell on 24 November and the Venetians and the crusaders sacked the city. Much of the city was demolished and its population escaped to the Croatian royal cities of Nin and Biograd na Moru, then noted as Jadera Nova (New Zadar). Two years later, most of the citizens returned to Zadar, after which the city was also referred to as Jadera Vetula (Old Zadar)
After spending the winter in Zadar the Crusaders continued their campaign, which subsequently led to the Siege of Constantinople. A number of contingents abandoned the Crusader army after the sack of Zadar. In 1203, Pope Innocent III excommunicated the entire crusading army, along with the Venetians but Zadar remained under Venetian rule. The siege and sacking of Zadar in 1202 had a major impact on the city, its economy and its people. Apart from the political effects of its status in the Kingdom of Croatia and Dalmatia; the destruction of the city had long-lasting effects on a city that was one of the major maritime and trade centres on the Adriatic Sea, a city which had the potential to rival the Republic of Venice and Dubrovnik.