Topic: Tell me a short, interesting fact about

One interesting fact about the Roman Empire is that the use of concrete in construction was pioneered by the Romans. Their secret ingredient for cement, known as pozzolana, was a volcanic ash from the area near Mount Vesuvius. This mixture, when combined with volcanic tephra, water, and lime, created a remarkably strong and water-resistant cement that they used to build many iconic structures such as the Colosseum and the Pantheon in Rome. The mortar and concrete used in these structures are remarkably durable and continue to stand almost 2,000 years later.