Pompeii is a town and has never erupted. Vesuvius is the volcano on the slopes of which is Pompeii and several other more current habitations.
Vesuvius has erupted many times.
I'm not sure how many times but i know about the famous eruption that burred a roman town of Pompeii it erupted over 2 days and many were killed , it took 4 years for Pompeii to be rediscovered. Hope...
The two recorded eruptions have been in 79 AD when it buried Pompeii and in 1944. The 1944 eruption was minor compared to the one in 79 AD. The volcano is still active, so it can erupt at any time.