What is the term for the central voussoir of an arch?

The term for the central voussoir of an arch is "keystone." The keystone is the topmost stone in an arch and plays a crucial role in its structural integrity. By being placed at the apex, it locks all the other voussoirs (the wedge-shaped stones that make up the arch) into position, allowing the arch to distribute weight effectively. This feature not only provides stability but also enables the arch to span greater distances compared to flat lintels. The design of an arch with a keystone has been widely used in various architectural styles throughout history, showcasing its importance in both aesthetics and engineering.

Other terms related to the options can clarify their meanings: springing stones are the first voussoirs that sit directly above the supports and start the curve of the arch; an architrave is actually a beam that rests on top of columns in classical architecture; a lintel is a horizontal support across the top of a doorway or window but does not have the same structural function as the keystone in an arch.