Two previous churches were built on the site of Hagia Sophia in Istanbul, Turkey. They were destroyed in 404 and 532 AD. The current masterpiece has a 185 foot dome. Construction required 10,000 workers and materials from quarries in Turkey, Syria, Egypt and Ephesus. When finished in 537, it was the world’s largest cathedral. 900 years later, the Sultan of the Ottoman Empire conquered Constantinople and converted the Byzantine cathedral into an Islamic mosque. In 1934, Hagia Sophia became a museum. Touring this landmark is an incredible excursion.