Dr. Thomas Keith

ANCIENT ARCHWAY

ca. 1855

The keystone is the wedge-shaped stone at the top of the arch that locks the other stones into place. How did builders keep the arch from falling until the keystone was put into place? A temporary support, usually of wood, was underneath and held the stones in place until the keystone was inserted. Then this temporary support was removed. The arch would not fall as long as its columns were steady and did not spread.