Turkey’s President Recep Tayyip Erdogan has decreed that the Hagia Sophia is to be used as a mosque. The Turkish leader took that step immediately after a court ruled that the conversion of the building into a museum, as part of the drive to secularize Turkey in the 1930s, was illegal. The renowned building, originally constructed by Christians for the Patriarchate of Constantinople, became a mosque in the 15th century when Muslims conquered the city.