Hagia Sophia is an iconic building located in Istanbul, Turkey, which has played several roles throughout its history. Its construction dates back to the time of Emperor Constantine the Great, and the first church was inaugurated on February 15, 360 during the reign of Constantius II. Known as Μεγάλη Ἐκκλησία-Megálē Ekklēsíā, "Great Church" in Greek-or Magna Ecclesia in Latin, this first structure was erected next to the imperial palace and surpassed in size the contemporary churches of the city.

The original church was inaugurated by the Arian bishop Eudosius of Antioch, but was burned and largely destroyed during riots in 404, during the exile of the patriarch John Chrysostom. After these events, Emperor Theodosius II ordered the construction of a second church in 415, which also suffered significant damage during the Nika riots in 532.

The third and current church, known as the Hagia Sophia that survives today, was built by order of Emperor Justinian I and was inaugurated on December 27, 537. Designed by the architects Isidore of Miletus and Anthemius of Tralles, this new basilica was notable for its monumentality and the use of materials from different parts of the empire. For centuries, Hagia Sophia served as the seat of the Orthodox Patriarch of Constantinople and the scene of Byzantine imperial ceremonies.

Throughout its history, the church experienced damage from earthquakes, fires and political events, but was restored and rebuilt on several occasions. In 1453, after the Ottoman conquest of Constantinople, Hagia Sophia was converted into a mosque by Sultan Mehmed II. In the 19th century, during the Ottoman period, important restorations were carried out under the direction of the architects Gaspare and Giuseppe Fossati.

In 1935, under the leadership of Mustafa Kemal Atatürk, Hagia Sophia was transformed into a museum as part of Turkey's modernization efforts. However, in 2020, President Recep Tayyip Erdoğan signed a decree to reverse the museum status and turn Hagia Sophia back into a mosque, triggering reactions both domestically and internationally.

This decision generated controversy and was criticized by various sectors, including UNESCO, but Hagia Sophia now functions as a mosque and is open to the public, retaining its historical and architectural elements, although some Christian mosaics are covered during Islamic prayers.