What is a pendentive?
A pendentive is a triangular, spherically curved surface that forms the transition between a square space and a circular dome. Four pendentives, each between two arches in a corner of the square, together create a circular rim on which the dome can rest.
The problem it solves is simple to state and difficult to build: a dome is round, a room is usually square. Something has to happen in the four corners.
The geometry
Imagine a hemisphere placed over the square so that the four corners of the square touch the sphere. Cut the sphere away along four vertical planes through the sides of the square. What remains in each corner is a curved triangle — the pendentive. Then slice the top off the hemisphere horizontally and you are left with a circular ring on which the dome proper, or a drum, can stand.
The load of the dome travels through the pendentives down to the four corner piers. There, alongside vertical load, a substantial outward thrust arises, which has to be taken by massive piers, half-domes or tie rods.
Pendentive versus squinch
There is a second solution to the same problem: the squinch, a small niche or splayed arch across the corner that turns the square into an octagon. A squinch bridges the corner; a pendentive creates a continuous curved surface. The pendentive gives a far smoother transition and allows a larger dome diameter.
Where you find them
The pendentive vault is the signature of Byzantine architecture; the Hagia Sophia in Istanbul (6th century) is the most famous example. Through the Renaissance and Baroque the motif spread across Europe, right into 19th-century domed churches, banks and exchange buildings. Because the surface is large and highly visible, it was often filled with mosaic, fresco or plasterwork — one of the most richly decorated spots in a domed interior.
Related terms
- Dome
- Drum
- Arch
- Vault
- Pier
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