15. Hagia Sophia: The world-famous Hagia Sophia is a 6th-century church-turned-mosque in Istanbul, and today it's a museum. Originally built in the 4th century AD by Constantine the Great, little remains of the initial structure, or the one built after it in the 5th century. What visitors now see dates to between 532 and 537 AD, raised in the Byzantine style under order of Emperor Justinian.
2. Ephesus: Ephesus was the Roman capital of Asia Minor, and home to over a quarter of a million people from slave traders to saints at its peak between 1 AD and 2 AD. The site of the Temple of the Artemis, which was one of the Seven Wonders of the Ancient World, 150 years of excavations at Ephesus have revealed the most complete Greco-Roman classical city on Earth. No wonder it was just added to the list of UNESCO World Heritage Sites.