Although some of the crusaders refused to take part in the siege, the attack on Zadar began in November 1202 despite letters from Pope Innocent III forbidding such an action and threatening excommunication.

[citation needed] Innocent III negotiated an agreement with the Republic of Venice, Europe's dominant sea power at the time, involving the construction of a fleet of warships and transports.

However, the first crusader groups did not leave France until April and May, others straggled along throughout the summer and some of the French nobles chose to sail instead from Marseilles and other ports.

[9] Therefore, after the Venetians had suspended their regular commercial operations for a year to build and crew the ships, only about 12,000 crusaders showed up at Venice to man and pay for them.

Boniface and the nobles added what money they could spare, and pledged their gold and silver plate to the Venetian moneylenders.

Zara had rebelled against the Venetian Republic in 1183, and placed itself under the dual protection of the Papacy and King Emeric of Hungary[11] (who had recently agreed to join the Crusade).

Though a large group of crusaders found the scheme repulsive and refused to participate, the majority agreed (despite the written protests of Innocent III), citing it as necessary to attain the larger goal of taking Jerusalem.

The Venetian warships were powered by 100 oarsmen each and featured metal-tipped rams just above the waterline as their primary weapons.

Chains and booms were laid across the mouth of Zadar's harbor as a defense, but the crusaders burst through them in their Venetian ships and landed their troops and equipment near the city, where they made a camp.

[17] Following the capture of the city, widespread violence erupted between the Frankish and Venetian contingents over the distribution of plunder.