Phlegrean Fields (Campi Flegrei)

The Phlegrean Fields (Campi Flegrei, meaning 'burning fields' in ancient Greek) constitute one of the world's largest and most scientifically significant active volcanic zones, covering approximately 150 square kilometres west of Naples in the Campania region of Italy. Rather than a single cone volcano, Campi Flegrei is a caldera supervolcano whose last major eruption in 1538 created Monte Nuovo—a new volcanic hill 123 metres high—in just two days. The entire area undergoes a geological process called bradyseism (slow vertical ground movement), which has caused the ancient Roman town of Puteoli (modern Pozzuoli) to rise and fall by several metres over the centuries, a process still actively measured today. The main visitor attractions are concentrated around Pozzuoli and the coastal area. The Flavian Amphitheatre (Anfiteatro Flavio) in Pozzuoli, the third largest amphitheatre in the Roman world with a capacity of 40,000 spectators, has some of the best-preserved underground machinery (hypogea) of any Roman arena. The Solfatara crater, a 770-metre-wide active volcanic depression near Pozzuoli, features steaming fumaroles, boiling mud pools, and sulphurous jets on a compacted white mineral surface—however the Solfatara site has been closed to visitors since a fatal accident in 2017 and access should be verified before any visit. Lake Avernus (Lago d'Averno), once believed by the ancients to be the entrance to the underworld and described as such by Virgil in the Aeneid, is now a tranquil lake within a volcanic crater where walking paths encircle the perimeter. Baia, an underwater archaeological site, contains sunken remains of Roman imperial thermal baths submerged due to bradyseism.