Omphalion

Marble was the material of choice for Imperial churches: it was believed to be created by earthy matter freezing in water that had sunk into the Earth's crust.

This omphalos dates from the Middle Byzantine, some five hundred years after the Hagia Sophia's if it is indeed an original feature, and is completely symmetrical in design.

The mosaics used tesserae of varying colors, texturized and oriented to reflect the light pouring in from the massive dome.

The effect of the sunlight shining through the windows surrounding the base of the dome hitting the tesserae would have been awe-inspiring.

[4] This view has been challenged over the years because of the dearth of textual reference from writers and travelers in the Byzantine Era.

Hagia Sophia herself has been altered so many times since the sixth-century that the Omphalion disappears and re-appears sporadically in the textual evidence that does exist.

[6] Historian Silvia Pedone does not attempt to assign a specific date to it, but she theorizes that it was arranged differently than what is seen today.

The marble omphalion from the floor of the Church of Hagia Sophia in Trabzon (north coast of modern Turkey) was brought to Thessalonica by Greek refugees in 1924.