Crusaders sent to recapture Jerusalem ended up sacking the largest Christian city in the world instead — and the Pope who launched them was horrified by what they did.
In 1198, Pope Innocent III called for a new Crusade to recapture Jerusalem from Muslim rule. The assembled army of French and Flemish knights contracted with Venice for transport ships — and immediately ran into trouble. They had wildly overestimated how many soldiers would show up. When the army finally gathered in Venice in 1202, there weren't nearly enough men to pay the agreed fare, and the Venetians refused to let them leave until the debt was settled.
Doge Enrico Dandolo — 90 years old, nearly blind, and nursing a deep personal hatred of Byzantium — offered a solution. Help Venice recover the rebellious Adriatic port of Zara first, and the debt would be forgiven. The Crusaders agreed. They sacked Zara in November 1202 — a Catholic city under the protection of the King of Hungary, himself a Crusader. Pope Innocent III was so appalled he excommunicated the entire army. The crusade hadn't reached the Holy Land, and it had already attacked a Christian city.
Then came the real diversion. A deposed Byzantine prince named Alexios offered the Crusaders an irresistible deal: help him retake Constantinople from his usurper uncle, and he would pay off their entire debt, provide troops, and submit the Eastern Orthodox Church to Rome. The Crusaders — still nowhere near Jerusalem — sailed for Constantinople. In the summer of 1203, they arrived at the greatest city in Christendom: a metropolis of 500,000 people protected by 20 kilometers of triple walls.
The first siege succeeded more easily than expected. The usurper emperor fled, Alexios and his father were restored, and the Crusaders set up camp outside the walls waiting for their payment. It never came. Alexios couldn't raise the money he'd promised. He ordered churches stripped of their gold icons and melted down for coin — an act that outraged his own people. In January 1204, Alexios was overthrown and strangled by a palace rival. The Crusaders were now outside the walls of the world's richest city, broke, with no patron and no plan.
On April 12, 1204, they attacked. Constantinople's defenses, weakened by months of political chaos, collapsed faster than anyone expected. For three days, the Crusaders — soldiers who had taken holy vows to fight for Christ — sacked the city. Byzantine historian Niketas Choniates wrote that the ancient Vandals and Goths 'would have found unbelievable' what the Latins did. They stripped the gold from Hagia Sophia, looted a thousand years of accumulated art and treasure, murdered civilians, and set fires that left tens of thousands homeless.
The treasures of Constantinople were scattered across Western Europe. Venice got the four bronze horses from the Hippodrome — they were installed above the entrance to St. Mark's Basilica, where replicas stand today. The original Holy Crown of Thorns, stripped from its reliquary, was later purchased by France's King Louis IX and housed in Sainte-Chapelle. The Crusaders never reached Jerusalem. They founded a 'Latin Empire' in Constantinople that lasted 57 years before the Byzantines reclaimed their city.
Pope Innocent III, when he heard what his Crusaders had done, wrote to them in fury: 'How, indeed, will the church of the Greeks return into ecclesiastical union when she has seen in the Latins only an example of perdition and works of darkness?' The Fourth Crusade didn't just fail to reclaim Jerusalem — it so weakened the Byzantine Empire that historians consider it a major contributing cause of Constantinople's fall to the Ottoman Turks in 1453, two and a half centuries later.