When the Ottomans had conquered Constantinople, they found a variety of Byzantine Christian churches, the largest and most prominent amongst them was the Hagia Sophia. The brickwork-and-mortar ribs and the spherical shell of the central dome of the Hagia Sophia were built simultaneously, as a self-supporting structure without any wooden centring. In the early Byzantine church of Hagia Irene, the ribs of the dome vault are fully integrated into the shell, similar to Western Roman domes, and thus are not visible from within the building. In the dome of the Hagia Sophia, the ribs and shell of the dome unite in a central medallion at the apex of the dome, the upper ends of the ribs being integrated into the shell; shell and ribs form one single structural entity. In later Byzantine buildings, like the Kalenderhane Mosque, the Eski Imaret Mosque (formerly the Monastery of Christ Pantepoptes) or the Pantokrator Monastery (today Zeyrek Mosque), the central medallion of the apex and the ribs of the dome became separate structural elements: the ribs are more pronounced and connect to the central medallion, which also stands out more pronouncedly, so that the entire construction gives the impression as if ribs and medallion are separate from, and underpin, the proper shell of the dome. Elaborately decorated ceilings and dome interiors draw influence from Near Eastern and Mediterranean architectural decoration while also serving as explicit and symbolic representations of the heavens. These dome shaped architectural features could be seen at the early Islamic palaces such as Qusayr ῾amra (c.712–15) and Khirbat al-mafjar (c.724–43).