Roman engineers discovered something extraordinary nearly 2,000 years ago—a form of concrete that doesn’t weaken with time, but heals itself and grows stronger. Structures built with Roman concrete, especially harbors and seawalls, continue to stand today despite constant exposure to seawater. Modern science has now uncovered why. Important Details: • Roman concrete was made using volcanic ash (pozzolana) instead of modern cement • When seawater enters cracks, it reacts with the ash • This react