The most important difference in Hagia Sophia’s architectural design is that its size and measurements are much larger than other churches, and the central dome is much bigger and higher. The dome that is over the central space is 55.60 m. from ground level, 31.87 m. from North to South and 30.87 m. from East to West. When constructing Hagia Sophia, architects have used marble, stone and special bricks that were light yet durable, specially made of Rhodes soil.
The dome that appeared compressed and spread out when it was first constructed, has been damaged in August 553 and December 557 due to earthquakes and in May 7, 558 the Eastern part of the dome has completely fallen apart. The renovation of the dome has been carried out by İsidoros’ nephew, young İsidoros. İsidoros has solved the problem by installing support systems through external braces and assisted the structure by adding forty windows and increasing the lenght of the dome by seven meters to make it smaller and lighter.
Hagia Sophia has survived a big fire in 859 and an earthquake in 869. The dome has collapsed after an earthquake in 989 and has been repaired. Due to the earthquakes in 1344 and 1346 a part of the dome and parts of the arch have collapsed and have been repaired.
The renovation process that has started by Fatih Sultan Mehmed during the Ottoman period has been continued by the following Sultans as well. The most important repair conducted in Hagia Sophia was by Sultan Abdulmecid’s (1839–1861) orders in 1847-1849 by the Swiss Fossati brothers. This repair included the filling of large cracks on the dome as well as securing the dome’s rim by implementing steel circles. During the renovations, one of the most important calligraphist’s of his time, Kazasker Mustafa İzzet Efendi has written the 35th verse of the quran on the main dome.