This map is part of a series of 12 animated maps showing the history of Crusades.
In August 1198, Pope Innocent III called a new crusade. Jerusalem was still in Muslim hands and the Crusader states were weakened.
Like Richard the Lionheart and Philip Augustus during the Third Crusade, the Western nobles chose to take the sea route to the East.
This would require a large fleet of ships and a contract was made with Venice to transport 30,000 crusaders in exchange for a hefty sum of money.
But the crusader army that converged on Venice in the summer of 1202 was far smaller than expected and could not raise the agreed sum. The old doge, Enrico Dandolo, agreed to cancel the debt if the crusaders helped him capture the city of Zadar on the Dalmatian coast. Once controlled by Venice, the city was now under the authority of the Hungarian king.
This proposal caused much dissent because the Hungarians were also Christians. Some crusaders abandoned the crusade and returned home, while others sailed directly to the Holy Land.
The bulk of the crusaders, however, accepted the doge’s deal and captured the city of Zadar in November 1202. The Pope, furious at the news, immediately excommunicated them.
The crusaders then made a port of call at Corfu, where they received a visit from Alexius IV Angelus, pretender to the imperial crown of Constantinople. He offered to pay their debt to Venice in exchange for help in regaining his throne.
In June 1203, the crusaders began the siege of Constantinople. On 17 July, they succeeded in seizing several sections of the city walls. The reigning emperor fled, and Alexius IV ascended the throne along with his father Isaac.
But in late January, Alexius IV was assassinated by a courtier who took his place as Alexius V. When the new ruler refused to respect the financial contract that his predecessor had made with the crusaders, the Crusader army attacked the city again.
On 12 April 1204, Constantinople was captured once more; this time, it was sacked. The Crusaders took treasures, statues and many relics and carried them back to the West, such as the famous Horses of St Mark in Venice.
The crusaders divided the empire among themselves and elected one of their number as Latin emperor of Constantinople. Venice took advantage of this situation to build up a vast maritime empire, in part by taking possession of Crete and the Ionian islands.
Several noble Byzantine families founded their own states in regions not controlled by the Latins; thus were created the Empire of Nicaea, the Empire of Trebizond and the Despotate of Epirus.
The Fourth Crusade had completely lost sight of its initial objective. The division of the Byzantine Empire benefited the Turks, who continued to control Asia Minor, and Venice, which had become the great maritime power of the day.