Pendentive dome

Pendentive is the term given to a construction element that allows a dome to be placed over square or rectangular spaces. Pendentives are triangular segments of a sphere that spread at the top and taper to points at the bottom, thereby enabling the continuous circular or elliptical base needed to support the dome. The horizontal curve of the dome’s base is connected directly to the vertical curves of the four supporting arches on each corner. Where the curve of the pendentive and dome is continuous, the vaulting form is known as a pendentive dome.

The pendentives receive the outward force from the dome’s weight and concentrate it at the four corners where it is directed down the columns to the foundations beneath. Prior to the development of pendentives, dome construction either demanded that the supporting structure was round, such as in Rome’s Pantheon, or were supported by corbelling or the use of squinches (a construction filling to form a base) in the corners of a room that allowed the dome to sit on top of four arches. Both of these methods limited the possible width and height of the dome. By directing force away from the walls, pendentive domes could be constructed much larger and higher.

The Romans were the first to experiment with pendentive domes in the 2nd-3rd century AD. They saw the supporting of a dome over an enclosed square or polygonal space as a particular architectural challenge.

Byzantine architects perfected the construction methods, and as a result pendentives are a common feature of Islamic architecture, often used with delicate ribbing. Pendentive domes were commonly built for Orthodox, Rennaissance and Baroque churches, in particular in Roman Catholic Europe and Latin America.

A major early example of a pendentive dome is the Hagia Sophia in Istanbul which was completed in AD 537. Another famous example is the Dome of the Rock in Jerusalem from the 7th century.

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