The Fourth Crusade set out as a work of piety: to win back the Holy Land for Christians. But the army had no money to pay the Venetians for its fleet, and the lofty aim soon began to be overgrown with calculation. First, in payment of the debt, the crusaders took a Christian city on the Adriatic for Venice; then they entangled themselves in a quarrel over the Byzantine throne, tempted by the promise of a lavish reward. Step by step the pilgrimage to the Holy Sepulchre became a venture of war and commerce, in which the question was no longer how to free Jerusalem but where to find plunder. The cross stayed on their shoulders, but it now served not Jerusalem — it served the debt and the hunger for gain.
In April 1204 this army, which never reached the Holy Land at all, stormed the greatest Christian city on earth — Constantinople. For three days the victors plundered the capital of their fellow believers: hauling vessels and relics out of the churches, stripping the covers from icons, breaking open the tombs, sparing neither the holy things nor the inhabitants. The city that for a thousand years had been the heart of Eastern Christianity was ravaged not by Muslims but by crusaders. On its site the victors founded their own Latin Empire and installed a Latin patriarch in Hagia Sophia — above the desecrated altar of the very church where the whole Orthodox East had prayed for centuries.
The captivity ran on for nearly six decades. Byzantium broke into fragments; the Latins sat in its capital while the Greek splinter-states fought for survival on the margins. Bled white by the disaster, the realm lost its men, its money, and its army — and never gathered its old strength again. In 1261 the Nicaean sovereign Michael VIII recovered Constantinople, restored the empire, and entered the reconquered capital as a liberator. But it was a return to ashes: the body of the empire was broken, the treasury empty, the borders full of holes — and into everything the empire felt toward the West there was now mixed, forever, the bitterness of betrayal.
In that fracture lies the law's quiet verdict. The blow struck in 1204 by fellow Christians proved deadlier than any blow from outside: it did not merely strip the city of its wealth, it drew out of the empire the reserve of strength it would need two and a half centuries later. When the Ottomans came up to the walls of Constantinople in 1453, they took a city already cut once at the root by the crusader sword. A pilgrimage turned to plunder had paid for another's victory over Christianity itself — and 1204 made 1453 all but inevitable.