The Romans started making concrete more than
2,000 years ago. In the later Roman eras, it was re-discovered that adding
volcanic ash to the mix allowed it to set underwater. They had a different
formula, which resulted in a substance that was not as strong as the modern
product. Yet structures like the Pantheon and the Colosseum have survived for
centuries, often with little to no maintenance. Geologists, archaeologists and
engineers are studying the properties of ancient Roman concrete to solve the
mystery of its longevity.