Siege of the Byzantine capital (mod. Istanbul, Turkey) by the army and fleet of the Fourth Crusade (1202-1204), culminating in the capture of the city on 13 April 1204.
The crusaders’ initial assault on the city in July 1203 resulted in the flight of the Byzantine emperor Alexios III Angelos and the crowning of the crusader-backed claimant to the throne, Alexios IV Angelos. Over the following months, however, relations between the Byzantine court and the crusaders were strained by Alexios IV’s inability to fulfill the obligations he had undertaken in return for the crusaders’ support. On 19 August, the day after a Greek riot against Latin residents within Constantinople, a band of crusaders attacked a mosque near the city’s harbor and started a devastating fire. By December the situation escalated into open conflict, as the Latins plundered the suburbs and the Greeks twice attempted to burn the crusader fleet.
Taking advantage of growing anti-Latin sentiment, in late January the Byzantine nobleman Alexios Doukas Mourt- zouphlos deposed Alexios IV, formally assuming the throne (as Alexios V) on 5 February 1204 and killing Alexios IV a few days later. Less ambiguous in his attitude toward the crusaders, over the following months Mourtzouphlos engaged the Latins in a number of skirmishes. This turn of events led the crusader fleet to attack the city walls along the Golden Horn (mod. Haliç) on 8 April 1204. The initial assault floundered, and the Latins retreated. Exhorted by the army’s clerics, who declared the assault a holy war against the murderous Alexios V and the schismatic Greeks, the attackers resumed their assault on 12 April. Two ships, the Paradise and the Pilgrim, succeeded in securing a tower on the harbor walls; Latin penetration into the city’s northern corner followed. That night, apparently in an attempt to defend their tenuous position, the crusaders in the city started another fire, which quickly raged out of control. His support wavering, Mourtzouphlos fled before dawn, leaving Constantinople open to the Latin army, which proceeded to sack the city on 13 April.
Taking of Constantinople.