Hagia Sophia, Turkey

  Hagia Sophia is the great architectural marvel at the heart of Istanbul, with its four minarets poised like moon-bound rockets. Constructed in the 6th century AD as an Orthodox church, it later became a mosque and, since 1935, a museum. This huge structure was built in just five years, and its musk walls are topped by an imposing dome, 31 meters wide by 56 meters high. The dome's base is ringed by windows, so that from within the structure, the dome seems almost to hover ethereally above the building.

  Famous in particular for its massive dome, it is considered the epitome of Byzantine architecture and is said to have changed the history of architecture. It was the largest cathedral in the world for nearly a thousand years, until Seville Cathedral was completed in 1520. The current building was originally constructed as a church between 532 and 537 on the orders of the Byzantine Emperor Justinian and was the third Church of the Holy Wisdom to occupy the site, the previous two having both been destroyed by rioters. It was designed by the Greek scientists Isidore of Miletus, a physicist, and Anthemius of Tralles, a mathematician.