What is the Roman material described as gravel and rubble in lime and sand mortar, capable of spanning great distances due to cohesion?

• A. Stone
• B. Concrete
• C. Brick
• D. Mortar

Answer: (B)

This describes Roman concrete. The Romans packed gravel or rubble into lime-and-sand mortar and bound it with a cementitious paste made stronger by volcanic ash (pozzolana), creating a cohesive mass. That cohesion lets the aggregate stay locked together under load, so the material can span large distances and form arches and vaults. This is different from solid stone blocks, which don’t rely on a binding paste, and from mortar alone, which lacks enough aggregate to span spaces. It’s also not bricks, which are individual units rather than a continuous, binding composite. The result is a durable, malleable material that enabled some of Rome’s most ambitious architectural forms.