Why did Mount Vesuvius cause so much damage?

Answer 1

Because they did not have the same knowledge of a volcano as we do today and could not outrun the eruption. If they weren't killed from the initial eruption, they would be killed by the ash and pumice rock that came pelting down from the sky. It wasn't safe for them to stay in their houses either because the pumice rock would accumulate and cause the house to cave in.

Answer 2

Vesuvius erupted in AD 79, burying Pompeii and its neighbouring city of Herculaneum under a pyroclastic flow. At the same time, a cloud of superheated gas, ash, and rock eruped from the volcano. In all, around 20,000 residents and visitors (it was the summer season, and many were holidaying there) were killed.

Prior to this, the volcano has been inactive for centuries, which is why cities had srpung up in its shadow, taking advantage of the fertile soil. The eruption in AD 79 was the result of an accumulation of centuries of underground pressures.

Vesusius erupted again in December 1631, this time destroying six villages and killing 4,000 people. Between 1631 and 1944, Vesuvius has erupted some 22 times.