Hagia Sophia (Greek: Ἁγία Σοφία, meaning the Holy Wisdom) is a mosque in the eastern Bosporus of Istanbul, Turkey. It was originally a Byzantine Eastern Orthodox cathedral and was turned into a mosque after the conquest of Constantinople by the Ottoman Empire. The walls and floor of the building are from the Late Antiquity and the decorations, including mosaics and frescoes, are mostly from the Middle Ages.