Historians have long said that the eruption of Mount Vesuvius, which famously buried the Roman city of Pompeii in volcanic ash, took place on 24 August 79 C.E. However, new excavations of the ruins have unearthed a charcoal inscription that puts that date—based on Pliny the Younger’s eyewitness account—into question, BBC reports. The inscription, probably made during a building renovation, includes the equivalent of the date 17 October 79 C.E. That suggests the explosion happened soon after, because ash from the eruption would have preserved the charcoal. Archaeologists now think that eruption might have occurred on 24 October.