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 like the Pantheon (which has the world's largest unreinforced dome) and the Colosseum 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. Now, scientists behind a new study say they have uncovered the mystery ingredient that allowed the Romans to make their construction material so durable and build elaborate structures in challenging places such as docks, sewers and earthquake zones.