Topic: Tell me a short, interesting fact about

One fascinating fact about the Roman Empire is that it was a pioneer in the use of concrete. The Romans developed a systematic method of making hydraulic concrete, which used volcanic ash in the aggregate mixed with lime and water. This innovation, combined with their engineering skills, allowed them to construct monumental structures such as aqueducts, roads, bridges, and buildings that still stand today, like the Colosseum and the Pantheon in Rome. Their concrete technology was a crucial part of their ability to expand and control such a vast empire.