In early August of 79 AD, springs and wells dried up, small earthquakes started taking place on 20 August, becoming more frequent over the next four days, but the warnings were not recognised, and on the afternoon of August 24, a catastrophic eruption of the volcano started. The eruption devastated the region, burying Pompeii and other settlements.
The only surviving reliable eyewitness account of the event was recorded by Pliny the Younger in two letters to the historian Tacitus. From his uncle's house in Misenum, approximately 35 km from the volcano, Pliny saw a large dark cloud (a pyroclastic flow) emanating from the mouth of the mountain. After some time the cloud rushed down the flanks of the mountain and covered everything, including the surrounding sea. Pliny stated that several earth tremors were felt at the time of the eruption and were followed by a very violent shaking of the ground. He also noted that ash was falling in very thick sheets and the village he was in had to be evacuated. Also, the sea was sucked away and forced back, a phenomenon which modern geologists call a tsunami.
His description then turned to the fact that the sun was blocked out by the eruption. His uncle Pliny the Elder had already taken several ships to investigate the phenomenon and to rescue people trapped at the foot of the volcano. Unable to land near the volcano because of an unfavourable wind and debris from the eruption, the elder Pliny continued to Stabiae about 4.5 km from Pompei, where he died the next morning.
Thick layers of ash covered two towns located at the base of the mountain, and eventually their names and locations were forgotten. Then Herculaneum was rediscovered in 1738, and Pompeii in 1748. These towns have since been excavated to reveal many intact buildings and wall paintings. The towns were actually found in 1599 by an architect named Fontana, who was digging a new course for the river Sarno, but it took more than 150 years before a serious campaign was started to unearth them.
The Forum, the baths, many houses, and some villas remained surprisingly well preserved. A hotel (of 1,000 square meters) was found a short distance from the town; it is now nicknamed the "Grand Hotel Murecine". Pompeii is the only ancient town of which the whole topographic structure is known precisely as it was, its streets are straight and laid out in a grid, in the purest Roman tradition, paved with polygonal stones, and have houses and shops on both sides of the street.
During early excavations of the site, occasional voids in the ash layer were found that contained human remains. Giuseppe Fiorelli had the idea of filling the empty spaces with plaster. What resulted were highly accurate forms of the doomed Pompeiani who failed to escape, in their last moment of life.