The Aya Sophia (Hagia Sophia) in Istanbul is one of the most overwhelming structures in the world. The edifice we see today was started in 532 by Byzantine Emperor Justinian I as a Christian cathedral. Its name – rendered variously as Aya Sophia, Hagia Sophia, Haghia Sophia or, in Turkish, Ayasofya – comes from the Greek (the language of the Byzantines), Άγία Σοφία, meaning "Holy Wisdom", a shortened version of the full name "Church of the Holy Wisdom of God". (The name is sometimes seen in English as "St. Sophia", but the church was not named after any saint; the Greek word "sophia" (σοφία) means "wisdom".)
The church was built on the site of two prior Christian churches: the Great Church, inaugurated by Emperor Constantius II in 360 and destroyed during riots in 404; and a second church (named Aya Sophia) begun by Emperor Theodosius II in 405 and destroyed in 532 during a revolt. After the destruction of the second church, Justinian ordered a much larger replacement and the structure we see today began to take form. Despite its enormous size and a dome which, at the time, was second in size only to the Pantheon in Rome, construction of the Aya Sophia was competed by 537. Disaster struck, however, in 558 when an earthquake collapsed the massive dome. By 562 a new dome was completed, extending the height by more than 20 feet to a total height of about 185 feet above the floor of the church.
The main dome of the Aya Sophia is an architectural marvel that seems to float above the interior thanks to a series of windows around its circumference that allow light to stream through. The dome is supported by four pendentives – inverted triangular sections that provide a transition between the round dome and the square layout of the room below – that transfer the weight of the dome to massive piers that rest on the floor. Pendentives would later be widely used in both Islamic architecture (such as in the large mosques in Istanbul) and in Europe. During its centuries as a Christian church, the Aya Sophia was lavishly decorated with golden mosaics and other art representing religious scenes. For more than 900 years, the Aya Sophia was the largest church in Christendom.
That role, however, came to an abrupt end in 1453 when the Turks conquered Constantinople (Istanbul) and the Church of the Holy Wisdom of God was converted into the Ayasofya Mosque (Ayasofya Cami). Over succeeding centuries Ottoman architects repaired, restored and added to the original structure. Aside from obvious additions, like the mihrab (niche that points to Mecca) and minbar (pulpit for Friday sermons) that are common to all mosques, the Ottomans added the sultan's loge inside and various sultans' tombs outside, along with an ablution fountain, a madrasah (religious school), kitchens to feed the poor and, most visibly, four minarets.
The minarets, as they stand today, are curious. The oldest, built in red brick, was added during the reign of Mehmed II (1451-1481) shortly after the Aya Sophia became a mosque. The slender stone minaret on the north was added during the reign of Selim I (the Grim) (1512-1520) by the prolific Ottoman architect Mimar Sinan, who also strengthened the mosque's walls with exterior buttresses. The two remaining minarets – which match each other, but neither of the two existing ones – were added during the reign of Murad III (1574-1595). Thus, today the grandeur of the Aya Sophia is unfortunately surrounded by a hodgepodge of mismatched minarets, none of which (with the possible exception of Sinan's) seem to fit with the building.
During its time as a mosque, the Aya Sophia's mosaics and other Christian symbols were either removed or, more fortunately, covered with plaster. Although Christianity and Islam share many religious figures – in particular, the Archangel Gabriel, who, in Christian belief, visited Mary to reveal that she will give birth to Jesus and, in Muslim belief, revealed the Qur'an to the Prophet Muhammad – Islam strictly forbids the creation of such images as a form of idolatry. Thus, even when the figures depicted in the mosaics were revered in Islam, their images were covered over.
In 1935, Mustafa Kemal Atatürk, the founder of the post-Ottoman Turkish Republic and its first president, ordered that the Aya Sophia should be a museum. Experts carefully removed the plaster and restored the mosaics and, for the first time in centuries, the original Christian imagery in the Aya Sophia was revealed to stand along side the Muslim features added later. Thus, the Aya Sophia may be one of the few places in the world where Christian and Muslim religious symbols stand side by side. Most remarkably, the mihrab from the Ayasofya Mosque now stands almost directly under a mosaic of Mary and Jesus from the Aya Sophia church. You don't see that juxtaposition every day!
Entering the Aya Sophia today is an overwhelming experience, even in an era when giant structures are commonplace. It is hard to imagine the impact this soaring edifice must have had on visitors in the sixth and succeeding centuries. It became the model for future Byzantine basilicas. It also served as an inspiration to later Ottoman architects who sought to match its splendor in Istanbul's two greatest mosques, Sinan's Süleymaniye Mosque, completed in 1557, and the Sultan Ahmet (or Blue) Mosque, completed in 1616.