While exploring a museum exhibit titled “A Day in Pompeii,” I was struck by the repeated theme that August 24, ad 79 began as an ordinary day. People were going about their daily business in homes, markets, and at the port of this prosperous Roman town of 20,000 people. At 8 a.m., a series of small emissions were seen coming from nearby Mount Vesuvius, followed by a violent eruption in the afternoon. In less than 24 hours, Pompeii and many of its people lay buried under a thick layer of volcanic ash. Unexpected.