A barrel vault is an architectural structure formed by extending a simple arch along a given distance. This design creates a continuous, tunnel-like space that can be used in various buildings, such as churches, cathedrals, and warehouses. The shape resembles a half-cylinder, providing strength and stability, which allows for larger open spaces without the need for many supporting columns. Barrel vaults have been used since ancient times, notably in Roman architecture. They are often made from materials like stone or brick, and their design can enhance acoustics and lighting within a space. Famous examples include the Pantheon in Rome and the Basilica of Maxentius.