A group of Pyrovile landed in the region and slept for thousands of years until awakened by an earthquake in 62AD. They set in motion a plan to xenoform the Earth into a planet of fire, to become their new home. In 79 AD, shortly before the volcanic eruption that was destined to destroy the city, the Tenth Doctor and Donna Noble arrived and foiled the Pyroviles' plan.
Unfortunately, to save the Earth, the Doctor and Donna were forced to trigger the eruption of the volcano, Vesuvius. The eruption completely destroyed the city and killed most of its population of twenty thousand people. Although Donna pleaded with the Doctor to rescue the population, he stated that the event was a crucial and unchangeable event in history, a fixed point in time. However, he agreed to save the Caecilius family from the destruction.
The eruption was so powerful that it briefly created a time rift, which by echoing back in time granted a number of Pompeii's citizens precognitive powers. (TV: The Fires of Pompeii)