While quite tragic, the two settlements of Pompeii and Herculaneum that sat at the base of Mount Vesuvius provide some of the best insight into ancient Roman society. In the first century AD these settlements and the people who inhabited them in their final moments were instantly devoured by the explosion of the volcano that they so wisely chose to build in front of.
As a result of being covered with layers of volcanic ash the settlements never had a chance to be looted throughout history and provides great insight into daily life in the Roman Empire. In Pompeii and Herculaneum everything is excavated exactly as the Romans left it, down to the dishes on the table. Other great examples of Roman art, roads, architecture, villas, baths and other structures are remarkably intact minus the present damage being done by tourists.
See Roman Cuisine
In addition to physical objects biological material was also preserved such as eggs, olives, almonds and more that can reveal valuable data about ancient agriculture. Overall the volcanic ash that helped bury Pompeii also helped preserve it and protect it from looters as well as natural decay of biological materials.