The story of Istanbul’s iconic domed Hagia Sophia reflects the city's turbulent history. It was built in 537 AD as an Eastern Orthodox cathedral – the world's largest church at that time. It remained under Christian control until 1453, when the conquering Ottomans converted the building into a mosque. Under the secular policies of Turkey's first President, Atatürk, the mosque was closed in 1931 and the building reopened as a museum that now welcomes millions of visitors per year. Visual highlights include the Byzantine dome's ornate ceiling and the blend of Muslim and Christian artworks that clothe the interior.