No trip to Istanbul will be complete without a trip to Hagia Sophia. It is not, as some may believe, dedicated to a Saint named Sophia. Rather, it is dedicated to the second person of the Trinity. For almost a thousand years, it was the largest basilica. It was also thousand years older than all the other great mosques in Istanbul.
The Hagia Sophia was actually the third church built on that spot, by the Byzantine Emperor Justinian, between 532 and 537. The nave (the main sanctuary) of the church ends in an apse, in the direction of Jerusalem.
After the Muslim conquest of Constantinople in 1453, Sultan Mehmet II converted into a mosque. A mihrab was installed in the direction of Mecca. Since both Jerusalem and Mecca are generally to the South-East of Istanbul, with Mecca to the south of Jerusalem, hence the mihrab is slightly to the right of the apse. Four minarets were also added outside the church.
The Muslims removed or covered up with cement most of the original mosaic depicting people such as Jesus, Mary, saints, and other famous people. On the dome at the top of the apse, however, a mosaic of Jesus and Mary was allowed to remain. Someone said it was because both Jesus and Mary appeared in the Koran, Jesus is considered a prophet while Mary is regarded as the holiest of women. But that still does not explain why most of the other images were destroyed except this on the apse. However, that decision created the fascinating juxtaposition of Mary and Jesus being flanked by 2 huge Islamic Calligraphic roundels bearing the names of Allah and Mohammed.
There are some mosaics which have been either preserved or uncovered. One depicts Jesus, Express Zoe and one of her husbands. Half of it is still covered in cement. I was told that restorers stopped removing the cement that covered the lower half for fear of damaging the mosaic.
Flying buttresses support the massive walls, which in turn support the dome. Without the buttresses, the walls would have collapsed outwards because of the weight of the huge dome.