The crater of the Astroni … is located in the middle-eastern area of the Phlegraean Fields.  As an elliptic caldera, it is 2 kilometres from east to west and about 1.6 kilometres from north to south. The inside is a wide depression, where they emerge some prominences: the so-called Colle dell’Imperatrice (Hill of the Emperess, 82 metres above the sea level), the Rotondella (73.8) and the Pagliaroni (54.1). The maximum height is of 255 metres, while the lower (9 metres) is at the level of Lago grande.

This volcano was born 3700 years ago, with a short activity. In its genesis we can recognize three phases: ascent of the magma from the conduct of alimentation, with formation of the lavic dome of Caprara; interaction of the magma with the water coming from the stratum, violent explosive emission of ashes, lapilli, pumices and wastes and formation of the crater; magmatic activity with a low explosiveness, with origin of the internal prominences.

The last volcanic manifestations were of fumarolic and hydrothermal kind. To these phenomena it is connected the exploiting of the sources of sulphuric water, already used as thermal station in ancient times. In the XIII century Pietro from Eboli mentioned them as Balneum Astruni, whose water was good particularly for suffering eyes, had a decongestant power and cured rheumatisms. In 1667 Sebastiano Bartolo located them near the lake of Caprara.

When they became royal reserve for hunting during the Aragonese Age, under Alfonso I, who surrounded them with a high embankment, Don Pedro de Toledo ordered to build in the Astroni the present  "Torre Centrale" (Central Tower) at the entrance with two levels and maybe other two towers, "Torre Lupara" and "Torre Nocera", with a sighting function.

The estate, alienated to private owners in 1692, was given to the Jesuits, who gave it to Carlo III of Bourbon. So it became again estate of royal hunting, and to that age they date back the boundary walls and the Vaccheria, used as a lodge.

Recently (25/04/1992), after many episodes, it was inaugurated the Natural Reserve of the State "Crater of the Astroni", managed directly by the WWF of Italy, supported by a Scientific and Technical Committee. For a repopulation and conservation of the local flora and fauna, as well as for a fruition of the Reserve, it has been created a Centre of Ambient Education.

The route is so limited to the bottom of the crater, being at present closed the one on the peak.

Paolo CAPUTO and Maria Rosaria PUGLIESE   " La via delle terme "