What are Roman arches made out of?

• A. Stone blocks and mortar
• B. Iron clamps
• C. Voussoirs and keystones
• D. Brick and plaster

Answer: (C)

Arch construction hinges on the way the pieces fit together under compression. In Roman arches, the curved span is built from wedge-shaped stones called voussoirs, cut so their sides form a precise curve. The keystone sits at the apex, locking the voussoirs together and transferring the load outward to the supports. This specific arrangement—voussoirs forming the curve and a central keystone locking them in—is what makes the arch strong and capable of spanning openings. While stone, mortar, bricks, or plaster might be involved in the surrounding structure, the defining components of the arch itself are the wedge-shaped voussoirs and the keystone.