In Byzantine architecture, a pendentive is the curved triangular surface that supports a dome over a square room.
Four pendentives transition from the square corners to the circular base of a dome. This allowed builders to place a large central dome over a square or nearly square bay, a major innovation in monumental Byzantine church design.
Pendentives differ from squinches, which use arches or corbelled construction to cut across a corner and create an intermediate polygonal base. Hagia Sophia in Constantinople is the best-known example of a monumental Byzantine building using pendentives.
The technique became especially important in the cross-in-square church plan, which spread widely through the Byzantine world. It also influenced later Ottoman architecture, although Ottoman architects developed the system in their own structural language.