pendentive, in architecture, a triangular segment of a spherical surface, filling in the upper corners of a room, in order to form, at the top, a circular support for a dome. The challenge of supporting a dome over an enclosed square or polygonal space assumed growing importance to the Roman builders of the late empire. It remained for Byzantine architects, however, to recognize the possibilities of the pendentive and fully develop it. One of the earliest examples of the use of the pendentive is also one of the largest—that of Hagia Sophia (completed ad 537) at Istanbul.