Located in Istanbul, the Hagia Sophia was originally a basilica constructed for the Eastern Roman Emperor Justinian I in the sixth century. A masterwork of Roman engineering, the massive dome (31 meters or 102 feet in diameter) covers what was for over 1000 years the largest enclosed space in the world. The church was looted by the fourth Crusaders in 1204, and became a mosque in the 15th century when The Ottomans conquered the city. The Hagia Sophia was converted into a museum in 1935 and is now one of the top attractions in Turkey.