How did Fatimid mosques in Cairo differ from earlier large hypostyle mosques?

Fatimid mosques in Cairo, such as Al-Azhar and Al-Ḥākim, generally maintained the traditional hypostyle plan with axial cupolas, consciously perpetuating the established aesthetic system of earlier periods. However, they introduced several notable innovations that distinguished them from earlier large hypostyle mosques:1

• Exterior Facade Composition: Unlike most earlier mosques, which lacked formal exterior emphasis, Fatimid mosques—particularly Al-Ḥākim—featured elaborately composed facades. These included corner towers and vaulted portals, marking a shift toward greater attention to the building's exterior appearance.1
• Monumental Small Mosques: The Fatimids developed monumental small mosques, such as Al-Aqmar, designed to serve local urban needs. While their internal arrangements remained traditional, their plans were adapted to available urban space and featured highly elaborate exterior decorations, exhibiting a level of conspicuousness not found in earlier large hypostyle structures.1
• Constructional Techniques: The Fatimids systematized the use of the four-centred keel arch and the muqarnas squinch. The latter became a primary architectural device for transitioning from a square base to a dome, becoming a hallmark of Egyptian decorative design.1