In the spring of 1218 the Fifth Crusade began in earnest when German crusader fleets landed at Acre. Along with King John, who was elected leader of the crusade, the fleets sailed to Egypt and besieged Damietta at the mouth of the Nile in May. The siege progressed slowly, and the Egyptian sultan al-Adil died in August 1218, supposedly of shock after the crusaders managed to capture one of Damietta's towers. He was succeeded by his son al-Kamil. In the autumn of 1218 reinforcements arrived from Europe, including the papal legate Pelagius of Albano. In the winter the crusaders were affected by floods and disease, and the siege dragged on throughout 1219, when Francis of Assisi arrived to attempt to negotiate a truce. Neither side could agree to terms, despite the Ayyubid offer of a thirty-year truce and the restoration of Jerusalem and most of the rest of the former kingdom. The crusaders finally managed to starve out the city and captured it in November. Al-Kamil retreated to the nearby fortress of al-Mansurah, but the crusaders remained in Damietta throughout 1219 and 1220, awaiting the arrival of Holy Roman Emperor Frederick II, while King John returned to Acre briefly to defend against al-Mu'azzam, who was raiding the kingdom from Damascus in John's absence. Still expecting the emperor's imminent arrival, in July 1221, the crusaders set off towards Cairo, but they were stopped by the rising Nile, which al-Kamil allowed to flood by breaking the dams along its course. The sultan easily defeated the trapped crusader army and regained Damietta. Emperor Frederick had, in fact, never left Europe at all.