semicircular arch

Arch in the form of a semicircle.

pier

Masonry upright that supports the arch.

intrados

Interior surface of the arch.

extrados

Exterior surface of the arch.

impost

Slightly projecting stone that surmounts the pier and supports the springer and the voussoirs.

springer

Stone that constitutes the arch’s first voussoir and is placed on top of the pier.

voussoir

Each of the stone wedges that make up the arch.

spandrel

Wall surface bordered by the curve of the arch, the start of another wall and the horizontal part above it.

keystone

Wedge-shaped stone in the center of an arch whose function is to balance the network of voussoirs.