Nevertheless, when the Venetians insisted on their payment, it turned out that there was not enough money for it. But the Doge Enrico Dandolo was not embarrassed to solve the problem. Instead of paying, the knights were allowed to finish their crossing. Venice had its eye on the Dalmatian port city of Zara, which could now be conquered with the help of the Crusaders. Many of them were reluctant to conquer a Christian city, but the Venetians had more leverage in this difficult situation. Even a ban on the Pope to divert the Crusade was ignored.
While the army was wintering in Zara, a tempting offer from Prince Alexios arrived. His father, Isaac II, had been Emperor of the Byzantine Empire before he was deposed and blinded by his brother. In return for the imperial throne, Alexius promised to pay the Crusader debts and provide military support. That was just the right thing for the Venetian doge. When only a minion of Venice sat on the throne, all trade in the region was in Venetian hands. No wonder then that the Doge supported the plan vehemently. The leaders of the Crusade also did not hesitate to follow their greed or their conscience. Thus, a fleet of 62 galleys with 4500 knights and 30,000 infantrymen came to sea in the spring of 1203 in the direction of Constantinople.
On July 17, 1203, the knights stormed the city and immediately began political reorganization. Isaac II was freed from his dungeon and appointed emperor together with his son. However, the leadership duo quickly realized that the Crusaders were not making any move to withdraw. The temptations of Constantinople were too great for the militants to risk their lives in Palestine and Egypt. However, the constant presence of the conquerors fueled the hatred of the population, and when the new rulers tried to collect the promised support for the occupiers, there was a violent uprising. In Byzantine tradition Alexios IV was murdered by his successor Alexios V. while his father was taken back to prison, where he died a few days later. The new Emperor tried to turn the wheel around again, but it was too late. Immediately, the Crusaders resumed the siege and stormed on April 13, 1204 the city for the second time. This time, there was no native throne candidate who wanted to save his population. In a three-day plundering orgy, the besiegers killed as in the bloodlust and destroyed irreplaceable art treasures in blind destructiveness. Subsequently, the city was divided among the winners. Balduin of Flanders became emperor by the grace of Venice and received in each case a part of the Reich territory as well as the city Constantinople. The ports came under Venetian control, and the occupied territories of Greece and Macedonia were distributed as fiefs.
The Fourth Crusade had irreparably damaged the Byzantine Empire, which for centuries had been a bulwark against the Turks. Although succeeded in 1261 to recapture Constantinople, but to old size Byzantine never returned. In the following Crusades, which were directed primarily against Egypt, Consantinople no longer played a role. The true winners of the Crusades were the up-and-coming Italian city states, especially Venice. Just as Byzantium was weakened by the two-front war on Muslims and Crusaders, the power of the lagoon city grew. With the conquest of Constantinople, the change of power was finally completed. The most famous symbol of the victory are four bronze horses, which the Venetians robbed from the city on the Bosporus. Copies of them are still standing above the central portal of the church of San Marco in Venice.