Alexios V had begun after his coronation to strengthen the defenses of Constantinople and ended negotiations with the Latins, disavowing Alexios IV's debt to the crusaders.

It is too late, however, for the new Emperor to make much of a difference.

An attempted surprise attack against the crusader camp fails despite the emperor's personal leadership.

During the ensuing fight, he defends the city with courage and tenacity, beating back the crusader assault of April 9.

On April 12, 1204, a strong northern wind aids the Venetian ships to come close to the wall.

After a short battle, approximately seventy crusaders manage to enter the city.

Some Crusaders are eventually able to knock holes in the walls, small enough for a few knights at a time to crawl through; the Venetians are also successful at scaling the walls from the sea, though there is extremely bloody fighting with the Varangians, at this time composed of English and Danes.

The crusaders capture the Blachernae section of the city in the northwest and use it as a base to attack the rest of the city, but while attempting to defend themselves with a wall of fire, they end up burning down even more of the city, leaving fifteen thousand people homeless.

The crusaders' second attack proves too strong to repel, and Alexios V flees into Thrace on the night of April 12, 1204, accompanied by Eudokia Angelina and her mother Euphrosyne Doukaina Kamatera.

Constantinople is under Latin control by the next day, the great city having for the first time in its long history; it is subjected by the foot soldiers to pillage and massacre for three days.

During the horrible and savage sacking inflicted on Constantinople by the crusaders, many ancient and medieval Roman and Greek works are either stolen or destroyed.

The magnificent Library of Constantinople is destroyed.

Despite their oaths and the threat of excommunication, the Crusaders ruthlessly and systematically violate the city's holy sanctuaries, destroying, defiling, or stealing all they can lay hands on; nothing is spared.

It is said that the total amount looted from Constantinople was about nine hundred thousand silver marks.

The Venetians receive one hundred and fifty thousand silver marks that is their due, while the Crusaders receive fifty thousand silver marks.

A further one hundred thousand silver marks are divided evenly up between the Crusaders and Venetians.

The remaining half-million silver marks are secretly kept back by many Crusader knights.

Many priceless icons, relics, and other objects will later turn up in western Europe, a large number in Venice.

The huge tenth-century altarpiece later known as the Pala d'Oro, as well as magnificent reliquaries, book covers, and four bronze horses (later to grace the entrance of Saint Mark's Basilica), are among the rich booty taken to Venice from Constantinople.

The Venetians and crusaders themselves take over the city and the government of the empire.

It is decided that twelve electors—six Venetians and six crusaders—should choose an emperor who will have one-quarter of the imperial domain.

The other three-quarters are to be divided.

The clergy of the party not belonging to the emperor elect are to have Hagia Sophia and choose a patriarch.

A small amount of property is specifically designated to support the clergy.

The rest is to be considered booty and divided.

Constantine Laskaris, one of the city's leading defenders, had meanwhile been proclaimed emperor in the Cathedral of St. Sophia as Constantine XI; he and other refugees now flee to Bursa.