Hagia Sophia is a former Orthodox

Eastern Orthodox Church

The Orthodox Church, officially called the Orthodox Catholic Church and commonly referred to as the Eastern Orthodox Church, is the second largest Christian denomination in the world, with an estimated 300 million adherents mainly in the countries of Belarus, Bulgaria, Cyprus, Georgia, Greece,...

 patriarchal

Patriarchate

A patriarchate is the office or jurisdiction of a patriarch. A patriarch, as the term is used here, is either* one of the highest-ranking bishops in Eastern Orthodoxy, earlier, the five that were included in the Pentarchy: Rome, Constantinople, Alexandria, Antioch, and Jerusalem, but now nine,...

 basilica

Basilica

The Latin word basilica , was originally used to describe a Roman public building, usually located in the forum of a Roman town. Public basilicas began to appear in Hellenistic cities in the 2nd century BC.The term was also applied to buildings used for religious purposes...

, later a mosque, and now a museum in Istanbul

Istanbul

Istanbul , historically known as Byzantium and Constantinople , is the largest city of Turkey. Istanbul metropolitan province had 13.26 million people living in it as of December, 2010, which is 18% of Turkey's population and the 3rd largest metropolitan area in Europe after London and...

, Turkey. From the date of its dedication in 360 until 1453, it served as the Greek Patriarchal cathedral

Cathedral

A cathedral is a Christian church that contains the seat of a bishop...

 of Constantinople

Constantinople

Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...

, except between 1204 and 1261, when it was converted to a Roman Catholic cathedral under the Latin Patriarch of Constantinople

Latin Patriarch of Constantinople

The Latin Patriarch of Constantinople was an office established as a result of Crusader activity in the Near East. The title should not be confused with that of the Patriarch of Constantinople, an office which existed before and after....

 of the Western Crusader established Latin Empire

Latin Empire

The Latin Empire or Latin Empire of Constantinople is the name given by historians to the feudal Crusader state founded by the leaders of the Fourth Crusade on lands captured from the Byzantine Empire. It was established after the capture of Constantinople in 1204 and lasted until 1261...

. The building was a mosque from 29 May 1453 until 1931, when it was secularized

Secularity

Secularity is the state of being separate from religion.For instance, eating and bathing may be regarded as examples of secular activities, because there may not be anything inherently religious about them...

. It was opened as a museum on 1 February 1935.

The Church was dedicated to the Logos, the second person of the Holy Trinity, its dedication

Consecrations in Eastern Christianity

Consecrations in Eastern Christianity can refer to either the Sacred Mystery of Cheirotonea of a Bishop, or the sanctification and solemn dedication of a church building. It can also be used to describe the change of the bread and wine into the Body and Blood of Christ at the Divine Liturgy...

 feast taking place on 25 December, the anniversary of the Birth of the incarnation

Incarnation (Christianity)

The Incarnation in traditional Christianity is the belief that Jesus Christ the second person of the Trinity, also known as God the Son or the Logos , "became flesh" by being conceived in the womb of a woman, the Virgin Mary, also known as the Theotokos .The Incarnation is a fundamental theological...

 of the Logos in Christ.