Squinch



In architecture, a squinch is a structural element used to support the base of a circular or octagonal dome that surmounts a square-plan chamber. Squinches are placed to diagonally span each upper corner where the walls meet. Constructed from masonry, they have several forms, including: a graduated series of stepped arches; a hollow, open half-cone (like a funnel) laid horizontally; or a small half-dome niche. They are designed to spread the load of a dome to the intersecting walls on which they are built. By bridging corners, they also visually transition an angular space to a round or near-circular zone.

Squinches originated in the Sassanid Empire of Ancient Persia, remaining in use across Central and West Asia into modern times. From its pre-Islamic origin, it developed into an influential structure for Islamic architecture. Georgia and Armenia also inherited the form from the Sassanids, where squinches were widely employed in buildings of all kinds. They are heavily featured in surviving or ruined medieval Christian churches of the region. An alternative approach to the structural problem of translating square space to round superstructure is the pendentive, much used in late Roman Empire and Byzantine architecture. Domes built in the Roman-influenced world utilised separately-evolved construction methods.



Middle East
The dome chamber in the Palace of Ardashir, the Sassanid king, in Firuzabad, Iran, is the earliest surviving example of the use of the squinch. After the rise of Islam, it remained a feature of Islamic architecture, especially in Iran, and was often covered by corbelled stalactite-like structures known as muqarnas. It was used in the Middle East and in eastern Romanesque architecture, although pendentives are more common in Byzantine architecture. The Hagia Sophia features both squinches and pendentives, in combination.

Western Europe
It spread to the Romanesque architecture of western Europe, one example being the Normans' 12th-century church of San Cataldo, Palermo, in Sicily. This has three domes, each supported by four doubled squinches.

Etymology
The word may possibly originate, the Oxford English Dictionary suggests, from the French word escoinson, meaning "from an angle", which became the English word "scuncheon" and then "scunch".