During the Middle Ages in the Campi Flegrei at least 40 hot springs, including that of the Solfatara, were active; some of them were already known in the Classical Age.
The thermal waters of the Solfatara were believed to cure the nerves, sight, fevers, skin diseases and infertility. The well presently visible was built in the early '800 to extract Alum from water pumped from the aquifer below, at about 10 metres deep. Prof. Sebastiano de Luca, known chemist at the University of Naples, accomplished around 1870 numerous scientific investigations on those waters which resulted rich in Alum, Sulphur oxides, Calcium Sulphates, Magnesium and other substances.
Water from the Solfatara has a characteristic and bitter lemon flavour. The mineral water was subsequently used to recover the ancient thermal activity which continued until the '20s. The depth of the aquifer that feeds the well varies in time and a relation between it and Bradyseismic phases is assumed.
The history of the Campi Flegrei is periodically crossed by phases of positive Bradyseism (raising of the ground) and negative (lowering of the ground); these slow movements have made to vary the level of the sea in the town of Pozzuoli by a few metres over the centuries.