The Hagia Sophia or Aya Sofia is a former mosque, and former church in the old European part of Istanbul. It was the leading church for the Eastern Orthodox church for over 900 years, until the sack of Constantinople in 1453, after which it was converted into a mosque. It remained a mosque for almost 500 years, as in 1935 it was converted into a museum by orders from the first president of Turkey: Atatürk. The builing has suffered a great bit of damage during the centuries (especially the dome), because of earthquakes and fires, but has always been rebuild soon after. A large numbers of the christian mosaics became visible in the 1930's, during restaurations.