Third Hagia Sophia brought some architectural deficiency even it was so pretentious in its era; in 558 east part of the dome, and in the earthquake of 869 one of the semi domes collapsed. The building damaged in the earthquake of 1344 was repaired with the special taxes and donations. Hagia Sophia faced the danger of collapsing completely in Ottoman era, but it was saved by the repair and supporting pillars of Mimar Sinan and managed to survive till today.
Magnificent dome in the center covers with semi domes over its axis; naves on both sides, flood abscissa, inner and outer narthexes following the entrance are the architectural features.
Main venue of Hagia Sophia is in the measure of 73.50 to 69.50. Dome sitting on pendants and carried by for large piers is 55.60 meters high and approximately 31 meters in diameter. The Interior of Hagia Sophia is decorated by 107 columns, 40 below, 67 above. On some of the elegant column headers, there are monograms of Emperor Justinian and Empress Theodora.
Hagia Sophia is famous for its decoration besides architecture. Figured mosaics of Iconoclasm period (726-843) were destroyed, so the mosaic seen belongs to post-Iconoclasm period, dated between 9th and 12th centuries. Mosaic board on Imperial Gate which is the biggest gate of inner narthex is dated to end of 9th century. On the Horologon Gate in the south of the inner narthex a mosaic board from 10th century, showing Constantine the Great giving the model of city and Justinian giving the model the church to Mary and Child Jesus, takes place.
Hagia Sophia receives daylight from 40 windows on flashing of the dome. On the four pendant’s that the dome stands on have figure of four-winged angels. Cubes in the center of the entrance are monolithic marble belonging to Hellenistic period, brought by Murat III (1574-1595) from Pergamum. Giant plates with 7,5 meters in diameter, hanging from the wall at gallery level are written by calligrapher Kazasker Mustafa Izzet Effendi.
Portrayal of Mary and Child Jesus on the semi dome of apsis is estimated to be the first mosaic to be done after Iconoclasm period. On the apsis vault, partially destroyed board of Archangel Gabriel is seen. On the left of the apsis maksoorah of the sultan made by Fossati in 1849, and on the right of the abscissa pulpit made in the 16th century are noteworthy.
Precious mosaics can be seen in the gallery of Hagia Sophia. This section is reached by a spiral ramp from the north of the inner narthex. There is a mosaic of Emperor Alexander (912-913) in the north gallery. Empress watched the religious ceremonies in the middle gallery covered by vault over the narthex. In this regard, it is known as the Empress Lounge.
Southern gallery is entered through a marble known as Heaven’s Gate. On the right after passing the door, Deesis Mosaic with size of 6 and 4, 7 meters from 12th century is one of the famous mosaics of Hagia Sophia. At the end of the gallery, there are two panels showing emperor and empress together with Mary and Jesus.