Arch design

Voussoirs

The wedge-shaped blocks used to create arches are called voussoirs. They must be precisely cut so that each adjacent block presses firmly against the next, and the load carried by an arch can therefore be properly transferred from one stone to another, and then down into the foundation.

The top central voussoir is called a keystone. It is always at the crown of an arch. As arches are constructed, support from below is required until the keystone is set in place. This construction method is called centering. Temporary wooden forms are put in place to support arches until a keystone is positioned. Essentially, an arch is built on a wooden model of itself, and then once the keystone is placed to finish the arch, the centering forms are removed.