A pendentive is a constructive device permitting the placing of a circular dome over a square room or an elliptical dome over a rectangular room. The pendentives, which are triangular segments of a sphere, taper to points at the bottom and spread at the top to establish the continuous circular or elliptical base needed for the dome. In masonry the pendentives thus receive the weight of the dome, concentrating it at the four corners where it can be received by the piers beneath. Prior to the pendentive's development, the device of corbelling or the use of the squinch in the corners of a room had been employed. The first attempts at pendentives were made by the Romans and full achievement of the form was reached in Hagia Sophia at Constantinople (6th cent.) by the Eastern Roman Byzantine Empire. Pendentives were commonly used in Renaissance and baroque churches, with a drum often inserted between the dome and pendentives.In addition, the pendentive is comprised of the geometric shape of a triangle this further makes a strong base to withstand the dome.
|(Click to enlarge)|
A triangular section of vaulting between the rim of a dome and each adjacent pair of the arches that support it.
[French pendentif, from Latin pendēns, pendent-, hanging, present participle of pendēre, to hang.]