In May 1182, the Massacre of the Latins turned Roman Catholic inhabitants of Constantinople into victims of a brutal uprising led by Andronikos Komnenos. This event shattered political relations between Western Europe and the Byzantine Empire for decades. Venetian merchants had carefully mapped Constantinople's harbours years before the sack, possibly anticipating its economic potential. Alexios IV Angelos, the son of deposed emperor Isaac II Angelos, persuaded Boniface of Montferrat and the Venetians to help him reinstate his father. He promised 200,000 marks of silver as payment, along with the submission of the Eastern Orthodox Church to Rome. The agreement also included provisions for expedition supplies and joining the crusade against the Saracens. On the 1st of August 1203, pro-Crusader Alexios Angelos was crowned Emperor Alexios IV of the Byzantine Empire. Riots broke out later that month between anti-Crusader Greeks and pro-Crusader Latins, lasting until November. Most of the populace began to turn against him during this period. On the 25th of January 1204, the death of co-Emperor Isaac II set off rioting in Constantinople. The people deposed Alexios IV, who then turned to the Crusaders for help. He was imprisoned by imperial chamberlain Alexios Doukas, who declared himself Emperor on the 5th of February. Alexios V executed Alexios IV by strangulation on the 8th of February.
Siege And Breach
By the end of March, combined Crusader armies were besieging Constantinople while Emperor Alexios V strengthened city defenses. From their encampment in Galata across the Golden Horn, forces prepared to attack. On the 9th of April 1204, Crusader and Venetian forces began an assault on the Golden Horn fortifications. Bad weather drove them back when troops landing came under heavy archery fire in open ground. Weather conditions finally favored the Crusaders on the 12th of April 1204 as skies cleared. A strong north wind aided Venetian ships near the Golden Horn to come close to the city wall. Attackers seized some towers along the wall after a short battle. Approximately 70 Crusaders managed to enter the city through holes knocked in the walls large enough for knights to crawl through. Venetians scaled the walls from the sea during extremely bloody fighting with Varangians. The Crusaders captured the Blachernae section of the city in the northwest. They used it as a base to attack the rest of the city. While attempting to defend themselves with a wall of fire, they ended up burning down even more of the city. Emperor Alexios V fled that night through the Polyandriou Gate into the countryside.