According to the biography of the 6th century Italian lawyer Antonion Castaldo, the swarm of earthquakes that had bothered the inhabitants of Pozzuoli and Naples all summer long ended abruptly on the eve of St. Michael (September 29) in the year 1538. Castaldo recalled that the end of this swarm was heralded by a very large earthquake followed immediately by loud thunder, sounding like bombardment from heavy guns. This was the beginning of a week-long eruption in Campi Flegrei, a volcanic caldera located along the west coast of southern Italy near Naples. 

This event has been the only eruption of Campi Flegrei in almost 4,000 years. It was preceded by a few decades of sporadic earthquakes swarms and noticeable uplift of the shoreline and was followed by 430 years of quiescence. Signs of renewed activity was first recognized in late 1969. Since then, the caldera center rose as much as 3 meters, and several hundred earthquakes were felt from 1983 to 1984 by people living in Campi Flegrei. These earthquakes extensively damaged buildings in Pozzuoli, located in the center of Campi Flegrei, and prompted the evacuation of 40,000 people. The uplift and the earthquakes stopped in December 1984, and no significant activity has occurred since.

We cannot forecast whether the activity since 968 will culminate in another eruption or whether Campi Flegrei will remain quiet for several hundred more years. This article summarizes the historical recorded of activity in Campi Flegrei, which, with varying degrees of reliability, spans 2,000 years, and emphasizes that further scientific studies of this caldera will improve our understanding of the behavior of longquiescent volcanic system.