The pyroclastic rocks abundant in the area around Mount Vesuvius were commonly used as building material already in Roman times. The Roman town of Pompeii, including most of its inhabitants, was buried under a several metres thick layer of tephra in the afternoon of 23 November 79 AD, after the plume emitted by a massive eruption of the volcano had collapsed. Despite massive destruction, many features have been preserved in the underground for almost two millennia. Excavations began in the 18th Century.