The Squinch As A Structural Solution

A squinch is a small arch, corbelled niche, or nested sequence of miniature arches built diagonally across each interior corner of a square chamber, converting the square into an octagon capable of carrying a circular or polygonal dome ring above it. Without some such device, a dome cannot rest directly on a square base, because a circle's circumference does not meet a square's corners; the squinch solves the problem by bridging each corner with enough masonry to approximate the missing arc, typically in two or three stepped tiers that visually announce the transition from straight wall to curved dome even as they perform the load-bearing work of the change.

In mosque architecture the squinch appears wherever a dome caps a square chamber, commonly over the bay directly in front of the mihrab, marking that space as the building's ritual focus through the visual drama of the transition zone as much as through the dome itself. Squinches are typically the most heavily decorated structural element in a domed chamber, since their stepped surfaces catch light and shadow in ways flat walls do not, and by the later medieval period many mosque builders replaced the plain squinch with the far more elaborate muqarnas, a related device built from many small nested cells rather than a few large arched tiers.