What architectural device is a squinch in Byzantine buildings?

In Byzantine buildings, a squinch is a corner arch or small structure that helps support a dome over a square space.

A dome is naturally circular, while a chamber below it may be square. Squinches solve that geometric problem by spanning or filling the upper corners, gradually converting the square plan into a shape suitable for the dome. They can appear as arches, niches, or short vaults.

Byzantine builders used squinches especially in churches and other domed structures, although the technique also appears in Persian and later Islamic architecture. It differs from a pendentive, which is a curved triangular surface suspended between the arches of a square bay.

The distinction matters because both devices perform a similar structural task. Hagia Sophia is famous for pendentives, while many smaller Byzantine churches and eastern architectural traditions display squinches more visibly.