Romans the Builders

Roman concrete lasted because of its ingredients and how it was mixed. Volcanic ash and lime reacted with water to form a strong, durable material. A 2023 MIT study found that hot mixing left small lime clasts that can heal cracks when water seeps in. The Pantheon's dome is still intact.

Roman aqueducts carried water by gravity alone. Engineers channeled clean water from distant springs along a gentle downward slope, using arched bridges to cross valleys and tunnels to pass hills. The longest ran for nearly 100 kilometers, and crews had to keep repairing leaks and clearing sediment.

Romans built roads in layers. Workers dug a trench about three feet deep, set stones at the bottom, covered them with gravel for drainage, and topped the road with flagstones set slightly askew to shed water. That layering kept roads strong and dry, which is one reason many stretches survive.

Arches spread weight outward and down, so a structure could span much wider gaps than a flat beam of stone. Roman builders used wedge-shaped arch stones called voussoirs to distribute the load. Stacked arches carried aqueducts across valleys, and the Alcantara bridge in Spain, about 182 meters long, still stands.