What is "pendentive"

Pendentive \Pen*den"tive\, n. [F. pendentif, fr. L. pendere to hang.] (Arch.)

1. The portion of a vault by means of which the square space in the middle of a building is brought to an octagon or circle to receive a cupola.

2. The part of a groined vault which is supported by, and springs from, one pier or corbel.

1727, from French pendentif (mid-16c.), from Latin pendentem (nominative pendens) "hanging," present participle of pendere "to hang" (see pendent (adj.)).

n. (context architecture English) The concave triangular sections of vaulting that provide the transition between a dome and the square base on which it is set and transfer the weight of the dome.

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. Pendentives were commonly used in Orthodox, Renaissance, and Baroque churches, with a drum with windows often inserted between the pendentives and the dome. The first experimentation with pendentives was made in Roman dome construction beginning in the 2nd–3rd century AD, while full development of the form was achieved in the 6th-century Eastern Roman Hagia Sophia at Constantinople.