Phlegraean Fields (flĬgrē´ən), Ital. Campi Flegrei, fertile volcanic region, Campania, S Italy, along the Tyrrhenian Sea between Pozzuoli and Naples. It is named for ancient Phlegra, in Macedonia, where in mythology the battle between the giants and the gods took place. In Roman times, the cities of Cumae, Baiae, and Puteoli (Pozzuoli) were fashionable watering places.
The region lies mostly along the northern side of an 8-mi-wide (13-km) volcanic caldera of the same name; most of the caldera is beneath the Gulf of Pozzuoli. The caldera was created by two large explosive eruptions, the first and more massive occurring about 36,000 years ago and the second about 15,000 years ago; both eruptions were far more destructive, with more wide-reaching effects, than those of Vesuvius to the west. A large number of eruptions subsequently occurred in three periods, with the last eruption occurring c.1650 BC More recent eruptions were at Solfatara (AD 1158) and Monte Nuovo (1538). Some of the region's many craters, cinder cones, and other volcanic features emit sulfurous vapors and mineral waters.