Who invented keystones? It is true that Egyptian, Babylonian, Greek and Assyrian civilizations used arches for underground structures such as drains and vaults. However, it was the Roman civilization (1000 BCE – 500 CE) that first began using a keystone (also called a capstone) in their arches.

A keystone is the wedge-shaped stone at the apex of a masonry arch or typically round- shaped one at the apex of a vault. In both cases it is the final piece placed during construction and locks all the stones into position, allowing the arch or vault to bear weight.