The Fonti San Felice (Saint Felix Fountains) is one of the most important hydraulic structures in the medieval city and consists of a large stone basin, partly dug into the ground, which is protected by a cover supported by two stone arches.

The construction leans against the hillside; the back and side walls are made of masonry.

Near the gate in the medieval walls, there are also some square blocks that were part of the Etruscan walls and, incorporated in this structure, a portion of cloaca for water drainage, which crossed the walls at this very point. Other hydraulic structures in front of the medieval springs indicate that this spring was also exploited in Roman times. A pipeline departed from here, supplying a cistern that served as a water reservoir for a spa town located further down; following the path from the medieval postern, we first find the cistern, now converted into a warehouse for agricultural tools, and then the Roman baths of S. Felice.

The Fonti San Felice was built in 1319, near the gate of the same name, but during renovation work carried out in 1979, numerous older remains came to light. An early phase of dwelling is documented by some remains of hut dating back to the 6th century B.C.; an Etruscan bronze statuette was found nearby the fountain, leading us to speculate on the presence of a place of worship dedicated to deities connected to water; furthermore, one of the communication routes with the territory must have started from here.

This fountain was commissioned by the citizens of Borgo Santo Stefano and built by Chelino Ducci Tancredi, as stated in the inscription placed on the shutter of the two large arches. Next to the fountain, as well as remains of Etruscan walls, there is an arch that native historians call Porta Romana, and which must have served as access to the nearby Terme Guarnacciane.