Design and Tradition / A short account of the principles and historic development of architecture and the applied arts

by Amor Fenn

The Keystone

A projecting block, or keystone, is sometimes used at the centre of the arch. The face width of its lowest edge should not be less than the width of the archivolt. Its height is not often less than one and a half times or more than twice this width.

It may be decorated in various ways, and is frequently in the shape of a console. This form is especially suitable when the keystone comes in contact with the architrave of the entablature, in which case it is capped with a moulded abacus.