The Deisis mosaic, frontal view, depicting Christ in the center, with the Blessed Virgin on the left and John the Baptist at the right; Hagia Sophia is a former patriarchal basilica, later a mosque, now a museum, in Istanbul, Turkey. Famous in particular for its massive dome, it is considered the epitome of Byzantine architecture. It was the largest cathedral ever built in the world for nearly a thousand years, until the completion of the Medieval Seville Cathedral in 1520. The current building was originally constructed as a church between 532 and 537 AD on the orders of the Byzantine Emperor Justinian, and was in fact the third Church of the Holy Wisdom to occupy the site (the previous two had both been destroyed by riots). It was designe...