During a hot and humid June in 1202, nearly twelve thousand Crusaders camped on the Lido of Venice, preparing to board a fleet of some four hundred major vessels bound for Egypt. They had taken the vow of the Cross many months earlier and had traveled from their homes across Western Europe to the city of the lagoons. Enthusiasm for their mission helped the warriors endure the heat and mosquitoes, for they had high hopes that they would soon disrupt Muslim power in Egypt and thereby restore Jerusalem to Christian control. But there was a rather large problem. During the preparations, the leaders of the Fourth Crusade (as it would come to be known) had contracted for a fleet and provisions sufficient for 33,500 Crusaders. Those hundreds of vessels and tons of foodstuffs now stood ready for departure. But the army that assembled in Venice was only a third of that projected size, which meant that the Crusaders lacked the...