On 12 April 1204 the Crusaders of the fourth Crusade attacked Constantinople.
(Click image for Wikipedia) The Crusaders looted, terrorized, and vandalized Constantinople for three days. The famous bronze horses from the Hippodrome were sent back to adorn the facade of St Mark’s Basilica in Venice, wherein they still remain. One of the most precious works to suffer such a fate was a large bronze statue of Hercules, created by the legendary Lysippos, court sculptor of no lesser than Alexander the Great. Like so many other priceless artworks made of bronze, the statue was melted down for its content by the Crusaders.
The Crusaders systematically violated the city’s holy sanctuaries, destroying or stealing all they could lay hands on; nothing was spared. The civilian population of Constantinople were subject to the Crusaders’ ruthless lust for spoils and glory; thousands of them were killed in cold blood. Women, even nuns, were raped by the Crusader army, which also sacked churches, monasteries, and convents. The very altars of these churches were smashed and torn to pieces for their gold and marble by the warriors who had sworn to fight in service of Christendom without question.
Most of the Byzantine aristocracy fled the city. The contemporary Byzantine historian and eye-witness, Nicetas Choniates closed his account of the fall of the city with the following description of a column of aristocratic refugees, including the Patriarch, making their way to Selymbria:
The peasants and common riff-raff jeered at those of us from Byzantium and were thick-headed enough to call our miserable poverty and nakedness equality…Many were only too happy to accept this outrage, saying “Blessed be the Lord that we have grown rich”, and buying up for next to nothing the property that their fellow-countrymen were forced to offer for sale, for they had not yet had much to do with the beef-eating Latins and they did not know that they served a wine as pure and unmixed as unadulterated bile, nor that they would treat the Byzantines with utter contempt.[14]
—Nicetas Choniates
The sack weakened the Byzantine Empire, which allowed neighboring groups like the Sultanate of Rum, and later the Ottoman Turks, to gain influence (see the Byzantine–Ottoman Wars).