thumb|250px|Squinches supporting a dome in [[Odzun Church|Odzun Basilica, Armenia, early 8th century]]
A squinch is a structural element in architecture used to support the base of a circular or octagonal dome above a square-plan chamber. Squinches are placed to diagonally span each of the upper internal vertices where the walls meet. When constructed from masonry, they have several forms, including a graduated series of stepped arches; a hollow, open half-cone (like half of a funnel laid horizontally, also called a trumpet arch); or a small half-dome niche. They are designed to evenly spread the load of a dome across the intersecting walls on which it rests, thus avoiding concentrating higher structural stress on smaller load-bearing areas. By bridging corners, they also visually transition a round or near-circular zone to an angular space. 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.
History
Western Asia
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 Western Asia and 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
The feature spread to the Romanesque architecture of western Europe. The earliest squinch still extant in Europe is the 5th-century Baptistery of San Giovanni in Fonte, Naples. A later example is the 12th-century Norman 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".
Gallery
<gallery>
File:Squinch.jpg|Conical squinch (trumpet arch) in the Palace of Ardashir in Fars province, Iran
File:Battistero di San Giovanni in Fonte- wall.JPG|Squinch in the Baptistery of San Giovanni in Fonte, Italy
</gallery>
See also
- Early and simple domes
- Persian domes
- Ancient Roman and Byzantine domes
- Splayed arch, an arch with conical intrados