The Hagia Sophia, formally known as the Hagia Sophia Grand Mosque (Ayasofya-i Kebîr Câmi-i Şerîfi) or with its former name, the Hagia Sophia Church is a mosque, an old basilica, a cathedral, and a museum located in Istanbul. It is a basilica-planned patriarchal cathedral built by the Byzantine Emperor Justinian I between 532-537 in the old city center of Istanbul’s historical peninsula. It was transformed into a mosque by Fatih Sultan Mehmed after the conquest of Istanbul by the Ottomans in 1453. Then it was converted into a museum with the Council of Ministers’ Decree published in 1934. After that its excavation and renovation works were started and it served as a museum between 1935-2020. In 2020, it gained the status of a mosque again after the cancellation of its museum status. Architecturally, the Hagia Sophia is a domed basilica-type structure that combines the central plan and is considered an important turning point in architectural history with its dome transition and load-bearing system features. The word “Hagia” in the name of the Hagia Sophia means “holy, saint”. The word “Sofia” comes from the Ancient Greek word “Sophos”, which means “wisdom”. Therefore, the name “Hagia Sophia” means “holy wisdom” or “divine wisdom” and is considered as one of the three attributes of God in the sect of Orthodoxy.It is stated that approximately 10,000 workersparticipated in the construction of the Hagia Sophia that was directed by Isidore of Miletus and Anthemius of Tralles, and a great fortune was spent by Justinian I for this work. One of the features of this very old building is that some of the columns, doors, and stones used for its construction were brought from other structures and temples which were older than the building.[ During the Byzantine period, the Hagia Sophia considered as having the great wealth of “holy relics”. One of these relics was a 15-meter-high silver iconostasis.The Hagia Sophia, which served as the patriarchal church for the Patriarch of Constantinople and was at the center of the Orthodox Church for a thousand years, witnessed the excommunication of Patrick I. Mihail Kirularios by Pope IX. Leo, and this event is generally regarded as the beginning of the Schism, which is the separation of the Eastern and Western churches. After the church was turned into a mosque in 1453, its mosaics containing human figures were not destroyed (those did not contain human figures were left as they are), but only covered with a thin plaster and remained under the plaster for centuries, in this way, it could be protected from natural and artificial destruction. While the mosque was being converted into a museum, some of the plasters were removed and the mosaics were brought to light again. The Hagia Sophia building seen today is also known as the “Third Hagia Sophia” because it is actually a church built on the same place for the third time. The first two churches were destroyed during the riots. The central dome of the Hagia Sophia, which is the widest dome of its era, collapsed once during the Byzantine period (May 7, 558), and it has never collapsed since Architect Sinan added the buttresses to the building. The Hagia Sophia is a tourist and spiritual attraction center for people from many different religious groups while being a pivot having a symbolic and cultural meaning for both Christians and Muslims.