At first the Fourth Crusade looked like all the other Crusades. In 1198, Pope Innocent III called for Christian knights to sail to the Holy Lands and re-capture Jerusalem, which Saladin had taken back from crusaders in 1187. In response to his call, thousands signed up, eager to fight Muslims in the Holy Lands and maybe accumulate a little plunder along the way. * Same song, fourth verse.
In fact, the Fourth Crusade took a wrong turn before it even began.** The leaders of the Fourth Crusade had negotiated with the Doge of Venice for enough ships to transport some thirty thousand crusaders at a cost of two marks per man and four marks per horse. The army that showed up in Venice in the summer of 1202 was one-third the size its leaders had prepared for. The crusaders were thirty-four thousand marks short of the agreed price..
The Venetians made an offer that the crusade leaders couldn’t refuse. Venice was having trouble with Zara, a rebellious Venetian outpost on the Dalmatian coast. If the crusaders helped subdue Zara on the way to the Middle East, they could pay their debt from captured booty. It was a perfect solution, if the crusaders were willing to ignore the fact that Zara was a Christian city under the protection of the King of Hungary, who was one of the crusaders.
From a crusading perspective, the attack on Zara was a disaster. (Why this came as a surprise to anyone is not clear.) The spoils of war found their way into the treasuries of individual lords instead of paying off the debt to the Venetians. And an outraged Pope Innocent excommunicated everyone involved.
Things got worse.
On January 1, 1203, ambassadors from Philip of Swabia contacted the crusade leaders with a proposal that would solve all their problems. If the crusaders would help a young Byzantine nobleman named Alexius Angelus regain the Byzantine throne, from which his father had been deposed, he would bring the Orthodox church back into the papal fold, pay the crusaders 200,000 silver marks and join the Crusade with ten thousand soldiers of his own. Putting Alexius Angelus on the throne would be a piece of crusader cake. His supporters would throw open the gates to their liberators.
Evidently the crusader leaders had never heard the phrase “if it seems too good to be true….” The Fourth Crusade headed to Constantinople, prepared to sack the seat of Orthodox Christianity in the name of Christianity, pay off the Venetians. and make peace with the pope. *** The discovery that Alexius Angelus had no supporters worth the name changed nothing. Faced with a rising tide of anti-western feeling in the city, the crusaders decided to take the city for themselves. In April, 1204, after three days of rape, pillage, and desecration, Constantinople was in the hands of the Fourth Crusade. It would remain the seat of a Roman Catholic regime until 1261.
* In fact, the leaders of the Fourth Crusade never intended to go to Palestine, a fact they did not share with the rank and file. The goal was Egypt, a wise move in military terms but without the emotional appeal of invading the Holy Lands.
**Even by the standards of people who considered crusades to be a good thing.
***Pope Innocent III did not approve. Learning of the crusaders’ intention, he sent a blistering letter in which he warned, “Let no one among you rashly convince himself that he may seize or plunder the Greeks’ lands on the pretext that they show little obedience to the Apostolic See.”