Structure / Masonry arch component
Keystone
/ˈkiː.stoʊn/noun
A compound of key and stone, describing the closing stone of an arch.
Definition
The wedge-shaped stone at the crown of a masonry arch. It completes the arch ring and is sometimes enlarged or decorated to emphasize the center of the opening.
Fig. 20 — Keystone: schematic studyNOT TO SCALE
Illustrative study — Keystone · AI-generatedSAMPLE IMAGE
Photo study — Keystone · AI-generated00:06
Structural & construction notes
The keystone is conventionally placed last while the arch is supported by centering. All voussoirs participate in transmitting compression; stability depends on the complete arch and adequate supports, not the keystone alone.
An educational reference. Project-specific design requires professional guidance.