The Roman city was thought to have been destroyed by a volcanic eruption of Mount Vesuvius on 24 August 79AD.
However, excavations have uncovered charcoal writing on a wall at the site that corresponds to the date October 17.
Archaeologists found the writing in a house that was under renovation just before the fatal eruption.
“Being charcoal, fragile and evanescent, which could not last a long time, it is more than likely that it was written in October 79 AD,” Massimo Osanna, head of the Pompeii site told reporters.
Italy’s culture Minister Alberto Bonisoli says the discovery is “extraordinary”.
“Today, with a lot of humility, maybe we’re rewriting the history books,” Mr Bonisoli says.
The original date of August 24 came from an account of the volcanic eruption that was written nearly 30 years after the event. Archaeologists now say Pompeii was destroyed in late October.
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