Definition & Meaning of "keystone"

What is a "keystone"?

In architecture, a keystone is the central stone at the top of an arch that holds the other stones in place. It is typically larger than the other stones and is shaped to fit perfectly into the arch's curve. The keystone plays a crucial role in distributing weight and maintaining the stability of the arch. Besides its functional importance, the keystone can also serve as a decorative element, often featuring unique carvings or designs. This feature enhances the overall beauty of the structure while providing essential structural support.