What happened?
Mount Vesuvius erupted in the year AD 79, burying the cities of Pompeii, Oplontis, and Stabiae under ashes and rock fragments, and the city of Herculaneum under a mudflow.
Mount Vesuvius, on the west coast of Italy, is the only active volcano in continental Europe and is thought to be one of the most dangerous volcanoes in the world.
Every single resident died instantly when the southern Italian town was hit by a 500°C pyroclastic hot surge.
Pyroclastic flows are a dense collection of hot gas and volcanic materials that flow down the side of an erupting volcano at high speed.
They are more dangerous than lava because they travel faster, at speeds of around 450mph (700 km/h), and at temperatures of 1,000°C.
An administrator and poet called Pliny the younger watched the disaster unfold from a distance.
Letters describing what he saw were found in the 16th century.
His writing suggests that the eruption caught the residents of Pompeii unaware.
Mount Vesuvius erupted in the year AD 79, burying the cities of Pompeii, Oplontis, and Stabiae under ashes and rock fragments, and the city of Herculaneum under a mudflow
He said that a column of smoke 'like an umbrella pine' rose from the volcano and made the towns around it as black as night.
People ran for their lives with torches, screaming and some wept as rain of ash and pumice fell for several hours.
While the eruption lasted for around 24 hours, the first pyroclastic surges began at midnight, causing the volcano's column to collapse.
An avalanche
