The Fifth Crusade began as a campaign by Western Europeans to reacquire Jerusalem and the rest of the Holy Land by first conquering Egypt, ruled by the powerful Ayyubid sultanate.

Cardinal Pelagius Galvani arrived as papal legate and de facto leader of the Crusade, supported by John of Brienne and the masters of the Templars, Hospitallers and Teutonic Knights.

Al-Kamil took advantage of this lull to reinforce Mansurah into a fortified city that could replace Damietta as the protector of the mouth of the Nile.

In December 1220, Honorius III announced that Frederick II would soon send troops, expected now in March 1221, with the newly crowned emperor leaving for Egypt in August.

Then in July 1221, rumors began that the army of one King David,[5] a descendant of the legendary Prester John, was on its way from the east to the Holy Land to join the Crusade.

On 24 July, the Crusader forces were relocated near the al-Bahr as-Saghit, now known as the Ushmum canal, south of the village of Ashmun al-Rumman, on the opposite bank from Mansurah.

One such canal near Barāmūn[8] could support large vessels in late August when the Nile was at its highest, and they brought numerous ships up from al-Maḥallah.

A naval squadron under fleet admiral Henry of Malta, and Sicilian chancellor Walter of Palearia and German imperial marshal Anselm of Justingen, had also been recently sent by Frederick II.

They offered the sultan withdrawal from Damietta and an eight-year truce in exchange for allowing the Crusader army to pass, the release of all prisoners, and the return of the relic of the True Cross.