The catastrophic event that occurred in the year 80 AD in the Roman Empire, affecting much of the population, was the eruption of Mount Vesuvius. This volcanic eruption led to the destruction of the cities of Pompeii and Herculaneum. The event buried these cities under ash and pumice, preserving them for centuries. The excavation of these sites has provided invaluable insights into Roman life and culture, making it a significant archaeological discovery.