Siege of Zara The Siege of Zara or Siege of Zadar ( ) ( November 10 – 24 , 1202 ) was the first major action of the Fourth Crusade and the first attack against a Catholic city by Catholic crusade rs . The Fourth Crusade sacked the Croatian town of Zadar , a rival of Venice , despite letters from Pope Innocent III forbidding such an action and threatening excommunication . Background . Shortly after his election as pope in 1198 , Pope Innocent III ( 1161 – 1216 ) published several papal encyclicals calling for the invasion and recapture of the Holy Land from the Muslims . His plan to accomplish this differed from the earlier ultimately unsuccessful Second and Third crusades in several ways . Instead of the secular nobles who led the earlier crusades , this one would be , in theory , completely under papal control . Innocent ' s plan also called for the invading armies to travel to Egypt by sea and seize the Nile Delta , which would then be used as a base from which to invade Palestine . His call was at first poorly received among the ruling families of Europe , but by 1200 , an army of approximately 35 , 000 was formed . 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 . The deal stipulated that about 35 , 000 crusaders would need transport and the Venetians would be paid 94 , 000 marks of silver , to be paid in instalments . A council held at Soissons in June 1201 chose Boniface of Montferrat to lead the expedition . The agreement between the Venetians and the crusaders had set the date for the arrival of the host in Venice before the end of April 1202 , in order to provide for a departure in time for a summer crossing at the end of June . However , the first groups did not leave France until April and May , and others straggled along throughout the summer . Some of the French nobles chose to sail instead from Marseilles and other ports . After the Venetians had suspended their commercial operations for a year to build and crew the ships , only about 12 , 000 showed up at Venice to man and pay for them . The leaders had counted on raising the money still owed the Venetians by through passage money from the individual crusaders . Boniface and the nobles added what money they could spare , and pledged their gold and silver plate to the Venetian moneylenders . The crusaders thus found themselves only able to pay 51 , 000 marks to the Venetians . In response , the Venetians indicated that they would accept the invasion of Zara ( now Zadar , Croatia ) , a Catholic city on the coast of the Adriatic , as well as nearby Trieste , in lieu of payment for the time being ; the crusaders were then to pay the rest owed to the Venetians out of their initial gains in the crusade . Zara had rebelled against the Venetian Republic in 1183 , and placed itself under the dual protection of the Papacy and King Emeric of Hungary ( 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 . In the winter of 1203 , Innocent excommunicated the entire crusading army , along with the Venetians , for taking part in the attack . " Behold , " the pope wrote , " your gold has turned into base metal and your silver has almost completely rusted since , departing from the purity of your plan and turning aside from the path onto the impassable road , you have , so to speak , withdrawn your hand from the plough [ . . . ] for when [ . . . ] you should have hastened to the land flowing with milk and honey , you turned away , going astray in the direction of the desert . " Pope Innocent was to later grant an absolution to the entire army . Transports and weapons . The attack on Zadar took the form of an amphibious landing followed by a brief siege . The incident was to foreshadow the Siege of Constantinople later in the campaign . The crusaders used the 50 amphibious transports , 100 horse carriers and 60 warships designed and built for them by the Venetians . Their transports were approximately 30 m long , 9 m wide and 12 m high , with a crew of 100 . Each one could carry up to 600 infantry . The horse carriers featured specially designed slings to carry their cargo of horses , and featured a fold - out ramp below the waterline that could be opened to allow mounted knights to charge directly onto shore . The Venetian warships were powered by 100 oarsmen each and featured a metal - tipped ram just above the waterline as their primary weapon . Also , during the siege , 150 siege engines were used to bombard the city ' s walls . 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 without harassment . Zadar fell on November 23 , 1202 .