The Dome in Hagia Sophia, Constantinople

Hagia Sophia, in Constantinople, is covered by a central dome with a diameter of 31 meters (102 feet). This crown for a dome seems rendered weightless by the unbroken arcade of arched windows under it, which help flood the colourful interior with light.

The dome is carried on pendentives: four concave triangular sections of masonry which solve the problem of setting the circular base of a dome on a square base. In Hagia Sophia the weight of the dome passes through the pendentives to four massive piers at the corners. Between them the dome seems to float upon four great arches. Such an endeavour was not practiced before in the world. The dome in Hagia Sophia is the first of its kind, being the largest dome in the Byzantine Empire.

In order to support such a structure and the massive dome, the nave was extended, adding semi domes. They brace the structure, solving the problem of weight and support. Thus a hierarchy of dome-headed elements build up to create a vast oblong interior crowned by the main dome, a sequence unexampled in antiquity.