Phlegraean Fields (flĭgrēˈən) [key], 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. Some of the region's approximately 30 craters still emit sulfurous vapors and mineral waters.