The Hagia Sophia ('Holy Wisdom') in Constantinople was the principal church of the Byzantine Empire.

The current structure was built by Emperor Justinian I in the 6th century CE in just five years.

Its most revolutionary feature is its massive central dome, which seems to float above the main space.

The architects, Isidore of Miletus and Anthemius of Tralles, used a system of pendentives to place the circular dome over a square base.

The interior was lavishly decorated with marble, intricate carvings, and magnificent gold mosaics.

A ring of 40 windows at the base of the dome floods the interior with light, creating a mystical atmosphere.

For nearly a thousand years, it was the largest cathedral in the world.

After the Ottoman conquest of Constantinople in 1453, it was converted into an imperial mosque, and minarets were added.

In 1935, the secular Turkish republic turned it into a museum.

It stands as the greatest surviving example of Byzantine architecture and a symbol of both the Byzantine and Ottoman empires.