Hagia Sophia Church was the former patriarchal basilica, a mosque and now a museum, Hagia Sophia is one of the greatest structures ever built. Created between 532 and 537 as a church on the orders of Justinian, emperor of the Byzantine Empire and home to many holy relics, Hagia Sophia was the Patriarchal church of Constantinople and the religious ground zero of the eastern Orthodox World for almost 1000 years.