What is plain arch?

A plain arch is a basic structural element in architecture and engineering, characterized by its curved shape that spans an opening and supports weight above it. It typically consists of a series of wedge-shaped stones or bricks, known as voussoirs, with the central stone called the keystone. Plain arches are primarily used in bridges, doorways, and Windows, and their design allows for the distribution of weight evenly, providing stability and strength. This simple yet effective form has been utilized in various architectural styles throughout history.