Pom·pei·i /pɒmˈpeɪ-i $ pɑːm-/ an ancient city in southern Italy, southeast of Naples, which was buried under the ash and lava (=hot liquid rock) from the volcano Mount Vesuvius when it suddenly erupted (erupt ) in 79AD. Everything was preserved exactly as it was then, because the ash and lava covered it completely. So when scientists started to dig the city up in the 18th century, they learned a lot about how ordinary people lived in Roman times.