The Phlegraean Fields (from the Greek word flègo, which means “brucio”, “ardo”) are a vast area located in the gulf of Pozzuoli, west of the city of Naples and its gulf. The area has been known since ancient times for its lively volcanic activity.
From a geological point of view, the area is a large caldera in a state of quiescence, with a diameter of 12-15 km, whose limits are given by the hill of Posillipo, from the Camaldoli hill, from the northern ridges of the crater of Quarto , the hill of Sanseverino, the acropolis of Cuma, and Monte di Procida. In this circuit there are numerous craters and small volcanic buildings (at least twenty-four), some of which have effusive gaseous manifestations (Solfatara area) or hydrothermal (in Agnano, Pozzuoli, Lucrino), as well as the phenomenon of bradyseism (very recognizable for the its entity in the past in the so-called Temple of Serapis in Pozzuoli). Throughout the area are visible important deposits of volcanic origin such as the Tufo Grigio Campano (or Ignimbrite Campana) or the Yellow Tuff. In the area there are lakes of volcanic origin (Lake Averno) and coastal lakes originated by barrier (Lake Lucrino, Lake Fusaro, and Lake Miseno).
In 2003, implementing the Regional Law of Campania n. 33 of 1.9.1993, the Regional Park of Campi Flegrei was established. The Phlegraean Fields are an area of high volcanic risk subjected to constant surveillance by the Vesuvius Observatory, both through periodic survey campaigns and continuous monitoring .
Important areas of biological and natural value are Capo Miseno, the submerged Baia Park, Monte Nuovo and the Astroni Crater. The Campi Flegrei area is included in the municipalities of Bacoli, Monte di Procida, Pozzuoli, Quarto, Giugliano in Campania and Naples. In particular, the first three municipalities mentioned, which occupy the so-called Flegrea peninsula, are almost completely Flegrei. The municipality of Quarto extends for the most part in the Phlegraean fields. The municipality of Giugliano instead extends in the Phlegraean fields limited to the area of Licola Mare, which is part of the Lago Patria hamlet. Finally, in the Phlegraean fields, the western part of the municipality of Naples falls, with the districts of Bagnoli, Fuorigrotta, Pianura, Posillipo, Soccavo and the towns of Agnano Terme (part of the Bagnoli district) and Pisani (part of the Pianura district).
The Phlegraean islands of Ischia, Procida and Vivara are part of the Phlegraean Fields, although they are located outside the original crater. They have a history and chronology partly different, partly parallel to that of the volcanoes on the mainland. In addition, numerous other craters have been identified in the Gulf of Pozzuoli, sunk into the sea or disintegrated by it over the millennia.