 The crusaders laid siege to Damietta , on the Nile , in May 1217 . Although they seized a strategically @-@ important tower on a nearby island on 24 August , Al @-@ Kamil ( who had succeeded Al @-@ Adil I in Egypt ) controlled traffic on the Nile . In September , reinforcements commanded by Pope Honorius III 's legate Cardinal Pelagius ( who considered himself the crusade 's supreme commander ) arrived from Italy . 
