821 years ago today, on April 12, 1204 (March 11, 1204 lunar calendar), the Crusaders sacked Constantinople. The Crusade invasion that took place in the Middle Ages was a war of aggression against the countries of the Near East by the Holy See, the knights of Western Europe and the great feudals of the Eastern Mediterranean countries. This war lasted for nearly two centuries from 1096 to 1270. Why is it called "the Crusade"? Because the war was started by the Roman Church, under the banner of anti-Islam, and the Western European troops who participated in the conquest wore a cross. In 1202, the Crusaders began their fourth invasion. Pope Innocent III's initial target for the attack was Egypt. But the Crusaders did not have ships to cross the sea and asked the merchants of Venice for help. The Venetian merchant oligarchy offered to take the city of Zadar as a condition of compensation, and the crusader leader accepted this condition. Zadar was Catholic, so the pope wrote a letter to scold the crusaders. At this time, Alexei, the son of the deposed Byzantine emperor Isaac II, asked the pope for help against the usurper Alexei III. So the crusaders marched on Byzantium under the pretext of helping Byzantium restore the "legitimate" throne. In June 1203, Alexei III absconded and Isaac II was restored to the throne. In order to pay the reward of the crusaders for helping to restore the throne, Alexei 200,000 silver marks and practiced extravagance, which aroused the uprising of the people of Constantinople, and Alexei was hanged. On April 12, 1204, the Crusaders attacked Constantinople. The city fell the next day. The Crusaders massacred unarmed residents, raped women, and looted property at will in the city. Most of the city's residents were massacred, dozens of perfect ancient carvings were destroyed, the rich collections of the Library of Constantinople were reduced to ashes, and the Church of St. Sophia was looted. Many art treasures were looted and could never be recovered. This was one of the crimes committed by the Crusaders in the East.