Concrete—cheap, durable, and versatile—was one of Rome's greatest contributions to architecture. Here, Tony Rook, a building materials specialist before he studied archeology, makes concrete the way the Romans might have.
An ancient recipe for concrete comes down to us from the Roman architect Vitruvius. The recipe calls for quicklime mixed with water, which turns into a fine powder. As more water is added, the powder becomes a putty that holds together the sand and small rocks that are added. The Romans added crushed tile or volcanic ash to waterproof the concrete, making it perfect for structures such as aqueducts and baths.