Voussoir

The springer is the lowest voussoir on each side, located where the curve of the arch springs from the vertical support or abutment of the wall or pier.

An enlarged and sometimes slightly dropped keystone is often found in Mannerist arches of the 16th century, beginning with the works of Giulio Romano, who also began the fashion for using voussoirs above rectangular openings, rather than a lintel (Palazzo Stati Maccarani, Rome, circa 1522).

The word is a stonemason's term borrowed in Middle English from French verbs connoting a "turn" (OED).

[citation needed] The outer boundary of a voussoir forms an extrados, internal - an intrados.

[2] In Visigothic and Moorish architectural traditions, the voussoirs are often in alternating colours (ablaq), usually red and white.