Hagia Sophia is one of the greatest surviving examples of Byzantine architecture. A former Orthodox patriarchal basilica, later a mosque, now a museum. The current building was originally constructed as a church between 532 and 537 CE on the orders of the Byzantine Emperor Justinian. For almost 500 years the principal mosque of Istanbul, Hagia Sophia served as a model for many of the Ottoman mosques. In 1935, Mustafa Kemal Atatürk, transformed it into a museum, the marble floor decorations and the mosaics appeared for the first time in centuries.