PENDENTIVE, in architecture, a triangular segment of a spherical surface, filling in the upper corners of a square, rectangular or polygonal room, in order to form, at the top, a circular support for a dome. Its intersections with the walls against which it abuts are semi-circles, and are usually carried by arches. The problem of supporting a dome over a square or polygonal hall was of continually growing importance to the late imperial Roman builders. This they attempted to solve, either by corbelling out the corners, projecting each course of masonry slightly over the one below, or by throwing across the corner diagonal arches or niches, which are known as squinches (q.v.). An early approximation of the pendentive form occurs in a domed room in one of the side buildings of the baths of Caracalla (A.D. 217). This form, however, was obtained by corbelling, whereas the true pendentive is built like a portion of a dome with radiating joints, and it remained for the Byzantine archi tects to recognize the possibilities of the form and give it definitive development. One of the earliest examples is also one of the
largest—that of the great church of S. Sophia at Constantinople (begun 532). Pendentives occur commonly in the domed Roman esque churches of Aquitania in France, as in S. Front at Perigueux (begun I I2o). They occur spasmodically in Romanesque work in Italy. During the Renaissance the development of domed churches gave great importance to the pendentive. Owing to Byzantine influence, pendentives are frequent in Mohammedan architecture, often decorated with stalactite ornament, or some times, as in Persia, with delicate ribbing. A vaulting form in which the curve of the pendentive and dome is continuous, with out a break, is known as a pendentive dome. (See BYZANTINE AND ROMANESQUE ARCHITECTURE; DOME.)