squinches

Squinch is an architectural device used to bridge the transition from a square plan to a dome or vaulted roof. It forms a transition at the corners of a square room, creating a base for a circular or polygonal dome without the need for pendentives. The result is a smooth transition in plan and elevation, and it can reduce the apparent unsupported span of the dome.

Squinches are typically constructed by projecting masonry at the corners in successive steps or by interlocking arches that join the corner supports. The two common forms are corbelled squinches, which stack cantilevered courses or blocks, and arched or muqarnas squinches, where a lattice of small arches or sculpted units fills the transition. The choice of form influences both the exterior silhouette and the interior experience of the dome.

Historically, squinches occur in several architectural traditions. They are especially associated with medieval Islamic architecture, where they offered a practical and decorative alternative to pendentives for mounting domes on square bases. They also appear in other regions and periods, including Persian, Central Asian, and some late antique contexts. In many buildings the squinch serves not only a structural function but also an ornamental one, with brickwork or stone carving emphasizing the corner transitions.

Related concepts include pendentives, which provide a different method for transferring dome loads to a square base, and muqarnas, which may be employed as decorative support within squinch structures.