It has long been held, on the basis of a letter of Pliny the Younger, that Mt. Vesuvius erupted on 24 August, AD 79. But after excavators began to work at the sites of Herculaneum at Pompeii, some scholars expressed doubts, suggesting a date later in the autumn of that year. Debate has increased with recent paleo-environmental research and the find of an inscription last year. Scholars have divided over a topic that might appear trivial—after all, most archaeological sites never enjoy such a precise date. But it is an excellent case study for testing our methods of historical and archaeological research, and I will lift the lid on those methods.