Innocent III calls the Fourth Crusade

November 15, 1199

Shocked by the failure of the earlier crusades and the death of Henry VI's planned expedition, Pope Innocent III issued the bull Post miserabile summoning a new crusade aimed at Egypt as the strategic key to Jerusalem. The expedition would instead sack Christian Constantinople. The diversion of the Fourth Crusade to Constantinople would prove the most consequential unintended consequence in the history of the crusading movement.