In time the side walls kept leaning outwards and the original low dome collapsed in 558. At later periods two times more the main doom was collapsed in 989 and 1346. The immediate restorations undertaken after the Turkish conquest in 1453 to convert it into a mosque saved this beautiful building. Among the major restorations at later times were the buttresses built by architect Sinan in the 16th century and the restoration by the Fossatti brothers in 1947-49. Hagia Sophia was converted into a museum by Ataturk order in 1935 after three years of restorations.
Hagia Sophia on Google Maps