Ascalon was the last city to fall to the Crusaders, who after seizing Jerusalem in July 1099 captured the remainder of Palestine one city at a time. Ascalon's resilience may have stemmed from the massive walls that the Fatimids had built around it, especially during the vizierate of al-Maʾmun al-Bataʾihi. The latter also commissioned shipyards for improving the Egyptian fleet and its ability to protect the empire's coastal regions. The thirteenth-century geographer Ibn Shaddad seems to undermine the effect of this project on Ascalon, explaining that the Franks could not capture the city for such a long time simply because of the lack of a harbour in which their ships could dock. Still, the later al-Qalqashandi (d. 820/1418) praises the Fatimids for the protection of their coastal borders and their concern with jihad; he lists Ascalon as one of the six cities that had been assigned fleets of nearly a hundred military ships and regiments of more than 5,000 registered well-paid warriors. Other contributing factors to Ascalon's late conquest by the Franks may have been the ethos of the ribāṭ and thughūr (that is, the religious merit of defending Islamic fortresses and garrison towns), which had been fostered in Ascalon for centuries; the frequent changing of the city's guards; and perhaps even – who knows? – its patron saint, al-Husayn ibn ʿAli.

In any event, as the gateway to Egypt, Ascalon was of considerable strategic importance to the Fatimids, and they held on to the city in the face of recurrent attacks on the part of the Latins. The latter were also well aware of the advantages of controlling the town, even though it lacked a proper port. Moreover, Ascalon's population had swelled with retreating soldiers and refugees, Muslim and Jewish, fleeing from places threatened or already captured by the Franks. According to William of Tyre, the Crusader historian, all these newcomers, even the children, were added to the military payroll with the objective of encouraging them to stay and defend the city. A Genizah letter, written shortly after the conquests of 1099, mentions that Jews from Fustat and Ascalon had raised money to ‘redeem the Scrolls of the Torah and … ransom the people of God who are in [Latin] captivity’ (in this order!).