The 1,500-year-old Hagia Sophia has undergone a long historical process of changes during three important periods. During the Roman Empire, Hagia Sophia was a Catholic church. During the Byzantine Empire, it was an Orthodox cathedral and under the Ottoman Empire Hagia Sophia was a mosque. (Mark & Cakmak, 1992) The structure has undergone multiple changes partly due to disasters such as fire and earthquakes. (Coruhlu et al., 2020) Also the conversion from church to mosque has led to multiple changes in the architectural structure and appearance of the building.
This thesis examines the architectural implications of the religious conversion of the house of worship. To investigate this, first a study will be done on the ar- chitecture of the church during the Byzantine Empire, then a study will be done on architecture of the mosque during the Ottoman Empire. From these results a comparison will be made which will highlight the architectural and aesthetic changes which Hagia Sophia has undergone as a result of the conversion and what effect the conversion has had on the appearance of the building.

Keywords - Hagia Sophia, architectural changes, religion, house of worship, church, mosque, Byzantine Empire, Ottoman Empire