The majestic structures of ancient Rome have survived for millennia — a testament to the ingenuity of Roman engineers, who perfected the use of concrete. But how did their construction materials help keep colossal buildings… standing for more than 2,000 years? Roman concrete, in many cases, has proven to be longer-lasting than its modern equivalent, which can deteriorate within decades. Scientists behind a new study, including researchers from the United States, Italy and Switzerland, analyzed 2,000-year-old concrete samples that were taken from a city wall at the archaeological site of Privernum, in central Italy, and are similar in composition to other concrete found throughout the Roman Empire. They found that white chunks in the concrete, referred to as lime clasts, gave the concrete the ability to heal cracks that formed over time. The white chunks previously had been overlooked as evidence of sloppy mixing or poor-quality raw material.