Two previous churches were built on the site of Hagia Sophia in Istanbul, Turkey. They were destroyed in 404 and 532 AD. Construction on the replacement required 10,000 workers and materials from quarries in Turkey, Syria and Egypt. When finished in 537, this was the world’s largest cathedral. The architectural masterpiece has a 185 foot dome. 900 years later, the Sultan of the Ottoman Empire conquered Constantinople and converted the Byzantine cathedral into an Islamic mosque. In 1934, Ayasofya became a museum and in 2020 it was restored to being a mosque. Hagia Sophia is an incredible landmark to visit.