When Mount Vesuvius erupted in 79AD it covered everything and everyone in hot lumps of lava and hot ash, killing everyone where ever they were at the time.
Excavations were started by Carlo Borbone in 1748 when and where ever he decided to dig. In 1861 Guiseppe Fiorelli started excavating in a more systematic way and he also started making plaster casts of the bodies he found. Pompeii was a very busy place at the time of the eruption in 79AD. Apart from the people who lived there, there was a continuous stream of sailors coming and going due to the fact that Pompeii was a main shipping port.