One of the greatest monuments of Byzantium, Hagia Sophia was built in the 6th century, but its exterior does not exhibit the characteristics of that century. The buttresses built to support the outer walls to ensure their endurance over the centuries, and the changes made during the Turkish era, have markedly altered the outer appearance.

Since it was used as a mosque for almost five hundred years after 1453, Islamic structures such as the minarets built on the corners of the main edifice, the fountain (sadirvan), mausoleum (turbe), and soup-kitchen (imare) etc. give Hagia Sophia a mosque-like appearance. Consequently, the 6th century architectural characteristics are much more apparent in the interior of the building.