Roman concrete, known as opus caementicium, was developed around 300 BC using lime, volcanic ash, and aggregate. Modern studies reveal that small lime pieces within the mix, called lime clasts, react with water seeping into cracks to form new mineral crystals, effectively healing the structure. Modern concrete sets quickly and relies on steel reinforcement, which can rust and cause internal damage over time. In contrast, Roman structures like the Pantheon and aqueducts have withstood centuries o