In the summer of 1219, a Crusader army had been encamped for over a year besieging the walled city of Damietta. At the start of the siege, the Sultan, al-Kamil, a nephew of Saladin (reign 1174–†1193), who had just succeeded his father Sultan Al-Adil I (reign 1200–†1218) as Sultan of Egypt, was encamped upstream of Damietta, unable to relieve it. A bloody and futile attack on the city was launched by the Crusaders on August 29, 1219, following which both sides agreed to a ceasefire which lasted four weeks. It was most probably during this interlude that St Francis and his companion Brother Pacifico crossed the enemy lines and were brought before the Sultan, remaining in his camp for a few days. The visit is reported in contemporary Crusader sources and in the earliest biographies of St Francis, but they give no information about what transpired during the encounter beyond noting that the Sultan received Francis graciously and that Francis preached to the Muslims without effect, returning unharmed to the Crusader camp. The Sultan, al-Kamil received him kindly. No contemporary Arab source mentions the visit. One detail, added by St Francis’ companion and biographer, friar Bonaventure (1221–†1274) in the official life of Francis (written in 1259, forty years after the event), is that St Francis offered to challenge the Sultan's "priests" (i.e. Islamic “Ulema” or “Sheikhs”) to trial-by-fire in order to prove the veracity of the Christian Gospel. Although Bonaventure asserts that the sultan refused to permit the challenge, subsequent biographies went further, claiming that a fire was actually kindled which Francis unhesitatingly entered without suffering burns.