In an arch, what is the top stone that locks the voussoirs in place called?

In an arch, what is the top stone that locks the voussoirs in place called?

• A. Keystone
• B. Wedge
• C. Abacus
• D. Spandrel

Answer: (A)

The central top stone of an arch is the keystone. It sits at the crown and locks the surrounding voussoirs into place, transferring their weight down to the supports. Once the keystone is set, the arch becomes a self-supporting, stable structure as the forces are redistributed along the curve. The other terms don’t fit: a wedge describes the shape of the individual stones, not the specific top piece; an abacus is the flat slab atop a column capital; a spandrel is the space or area beside and above the arch.

The central top stone of an arch is the keystone. It sits at the crown and locks the surrounding voussoirs into place, transferring their weight down to the supports. Once the keystone is set, the arch becomes a self-supporting, stable structure as the forces are redistributed along the curve. The other terms don’t fit: a wedge describes the shape of the individual stones, not the specific top piece; an abacus is the flat slab atop a column capital; a spandrel is the space or area beside and above the arch.