This paper attempts to draw together all relevant textual, archival, and archaeological information concerning the appearance of Jerusalem's Fāṭimid and Seljȗk city defenses, including its multiple fortification walls and towers, ditches and outworks, on the eve of the Crusader conquest of that city in July 1099. What were the physical defensive impediments preventing the Crusader forces from getting close to the walls and gaining quick access to the city? Analysis of the textual sources is provided in this paper. What did the ditches and outworks look like, and how formidable were they? Details are provided based on recent archaeological excavation results, as well as from an examination of archival materials, some hitherto unpublished. New data is presented on the physical appearance and chronology of the previously unknown and elusive sunken ditch on the brow of Mount Zion at the spot where Raymond of St. Gilles laid siege to the city from the south. The paper also deals with what eventually transpired to the fortifications of Jerusalem under subsequent Frankish and Ayyȗbid rule. As we shall see, in the aftermath of Ṣalāḥ al-Dīn's conquest of the city in 1187, it appears that Jerusalem came to be protected from the south by two separate fortification walls.