Topic: Tell me a short, interesting fact about

One intriguing fact about the Roman Empire is that it was also a pioneer in the use of concrete. Roman concrete, called Pozzolana, was a mixture of volcanic ash, lime, and water. It was strong, water-resistant, and remarkable for its ability to withstand use in areas underwater. The Romans used this concrete to build structures that still stand today, such as the Colosseum, Pantheon, and many of their aqueducts. In fact, their building techniques were so advanced that parts of the Roman concrete structures are still intact after more than 2,000 years.