Glossary · K
Keystone
Also called key
The central voussoir at the crown of an arch, the last to be set; it locks the ring. Pointed arches often have a joint at the apex instead.
See also: Voussoir
Rules that use the word
Wedges that lock by their own weight. Build an arch of wedge-shaped stones (voussoirs) whose joints all point towards the centre of the curve: each stone can then fall only by forcing its neighbours apart, and so the ring holds itself up once the last stone, the keystone, is in place.
Every arch is first built on a frame. An arch cannot support itself until it is complete. Build it on a timber centring shaped to the intrados, strike the centring only when the keystone is set and the mortar has taken, and reuse it from bay to bay, which is one reason to keep the spans of an arcade equal.
Where it appears in the book
In the chapters The Arch, Renaissance and Baroque.
A feature of Postmodernism architecture.
Nearby in the glossary
Karesansui · Karikomi · Katsuogi · Ken · Kirizuma · Kiwari · Knot garden · Kokoshnik