Old Cairo contains the remnants of those cities which were capitals before al-Qahira, such as Fustat, al-Askar and al-Qatta'i. These are the location of the Mosque of Amr and the Mosque of ibn Tulun, though little else remains today. This area also encompasses Coptic Cairo and its many old churches and ruins of Roman fortifications. Modern tourists visit locations such as the Coptic Museum, the Babylon Fortress, the Hanging Church and other Coptic churches, the Ben Ezra Synagogue and the Mosque of Amr ibn al-As. Fort Babylon is a Roman fortress around which many of the Egyptian Christians' oldest churches were built.
https://en.wikipedia.org/wiki/Old_Cairo