The geographer Strabone (I century B.C.) called Hephaiston (square of Hephaestus, in Latin Forum Vulcani), the most famous and typical crater of the Phlegraean Fields.

… It's already thanks to Petronio (middle of the I A.D.) that we have a representation of the volcanic activity, described with dim views, … but certainly inspired by the suggestive scenery that he had before his eyes:

"There is, between Neapolis and the vast fields of Dicearchia, a place located in the bottom of a hollow abyss, washed by the waters of Cocito; in fact steams come out of it violently, and spread around with choking heat. Never in autumn this land turns green, nor the fertile ground let grass grow, never in spring the tender bushes resound of the dissonant harmony of the warbling of birds; but squalor and rocks covered with black lava rejoice, surrounded by the funereal cypress. (Satyricon, CXX,67-75).

Born about 4000 years ago and situated almost in the middle of the Phlegraean Fields, the Solfatara (whose name comes from the late Latin Sulpha Terra – land of sulphur) is a volcano more recent than the ones of Agnano and Astroni. Its fumarolic  manifestations, the cyclic deformation of the soil and the seismic shakes are the suggestive aspect of its active volcanism.

Of a "monogenetic" kind, that is formed by a unique event and in a limited space of time, it feeds no more on magma. The chronicles mention another eruption, happened in 1198. Probably this eruption involved only the water-bearing stratums, as it is demonstrated by the archaeological recoveries of 1980 on the slopes of the south-west side of the volcano, as the graves found there were placed in the volcanic materials of the age of the eruption.

… At present, after the bradyseismic crises of 1970-72 and 1982-84, the activity of the Solfatara, a perennial danger for the surrounding urban areas, is guarded by a vast web of instruments and the volcano is considered by scientists as a natural laboratory for geologic researches.

… The volcanological Observatory, a small building located in proximity to the fumarole called Bocca Grande, was erected at the beginning of the XX century by the Berlinese volcanologist  Immanuel Friedländer.

In 1810-1855 the Solfatara, a royal property, was exploited as cave to extract some chemical compounds used for military aims. Many of these compounds, made of sulphur and other minerals, can be seen still today turned into patinas, crusts and crystals, near the fumaroles, generated for sublimation by the hydrothermal activity of the volcano.

It is possible to accede to the Solfatara from the entrance of a building dating back to last century. Passing an area which is partly woody, partly used as a camping, you arrive to the crater. Here the soil is characterized by the whitewash, an argillaceous-siliceous material, which depurated was used, already in Roman Age, to extract the alum.

Walking along the inner perimeter anticlockwise, you can seen the south-west side: at its base they appear on the surface the dark red volcanic lavas, which above are covered with lighter products of the more recent eruptions.

The Mediterranean vegetation, contrasting with the colours of the soil and of the sides, at intervals covers the sides and the north part of the crater. Then you arrive to the fumarole of Bocca Grande, enclosed after the opening of other minor and surrounding fractures, where it is more intense the show of the volcanic activity.

Going on you meet another building, endowed with two arched structures, used as natural sudatoria thanks to the exploitation of hot steams. In the surrounding area there are heather, cistus, arbutus and myrtle, suitable plants for the particular kind of soil and environment.

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