Squinch

A squinch is an architectural device used to support a dome over a square or rectangular space by creating a transition from the plan to a circular or polygonal base. In a true squinch, arches or lintels are built across the corners of the square, forming a platform that transfers the weight of the dome to the surrounding walls. The resulting top can be circular or polygonal, providing a foundation for the dome.

A second form, the corbel squinch, relies on projecting courses of masonry or brackets at the corners. These corbels or stepped elements extend beyond the original plan, gradually narrowing as they rise to form a base for the dome. Both forms aim to solve the structural problem of seating a circular dome on a square plan without using pendentives.

Squinches are distinguished from pendentives, which transfer load from a circular dome directly to a rectangular or square base through a continuous curved transition. Squinches create discrete transitional elements at the corners, whereas pendentives form a smooth, curving surface across the interior walls. In practice, squinches may be visible as a decorative system of arches or brackets, or they may be integrated into the wall structure in a more concealed fashion.

Historically, squinches appear in various architectural traditions, including Byzantine and Islamic architecture, and were used in medieval and Renaissance contexts as designers explored different ways to crown square spaces with domes. Today the term remains a technical designation for this corner-based method of supporting a dome.