Some history of Pompeii:
The ruins of Pompeii lie about 5 miles from Mount Vesuvius and roughly 17 miles from Naples in the region of Campania, inland and close to the modern town of Pompei (written with a single "i"). At the time of the eruption of Vesuvius the town would have been a lot closer to the coast and is estimated to have covered more than 160 acres.
The eruption of the Vesuvius volcano buried Pompeii under metres of ash and pumice, a blanketing so comprehensive that the site was effectively lost for 1700 years; it was not the ash that killed the townsfolk however, it was the heat, with hot surges reaching 250 degrees centigrade bringing instant death, even to those hiding indoors.
What is so remarkable about the ruins of Pompeii is the incredibly complete, fresh, vivid and intimate insight they give us into the daily life of a Roman city at the height of the Roman Empire. The eruption lasted for more than 24 hours and, at least to begin with, allowed an escape for those that decided to flee unburdened. Those that stayed are frozen [sic] in time and place, huddling inside, clutching their loved ones or their wealth, curled up and hiding, to no avail.
There are amazingly well preserved homes, villas, markets, a forum, baths. Frescoes shine a light on the goings-on of everyday life, and preserved everywhere are mundane details of how the estimated 20,000 inhabitants lived almost 2000 years ago.
Just how many survived is not known, but even by Roman standards, the eruption of Vesuvius was a catastrophe. Well used to rebuilding cities in the wake of earthquakes, the Romans simply didn't bother with Pompeii (ditto nearby Herculaneum), so great was the devastation. What they did do was plunder the ruins - excavations have uncovered numerous tunnels beneath the carapace of dust and pumice, burrowing from villa to villa, smashing through walls to loot the treasures within, greatly reducing the number of objects that would otherwise have been discovered.
Pompeii was a wealthy town, rich on agriculture from the fertile lands around, packed with holiday villas of wealthy Romans, a key port and vacation destination, well known to Greek and Phoenician sailors, fought for and conquered by numerous peoples across the centuries.
It was in 1738 that nearby Herculaneum was properly rediscovered (by accident, during building works), and in 1748 that Pompeii saw the light again, intentionally excavated by a Spanish military engineer. In the 1860's began the technique of filling the hollows, the imprints of entombed and subsequently decomposed corpses with plaster, creating perfect images of some of the dead. These haunting casts are on show both at Pompeii and at the Archaeological Museum in Naples.
Notwithstanding the fact that excavations have largely halted and that the areas open to visitors are fewer than they were 50 years ago, it is still possible to range far and wide, easily filling a day immersing yourself in the Roman Empire at the height of its glories. You may wish to read a bit more here: Pompeii, a UNESCO World Heritage site