The building, spread over multiple levels, supplied by the Serino aqueduct and mainly constructed in opus vittatum and latericium, dates back in its original layout to the first half of the 2nd century AD; however, it underwent multiple interventions over time that altered the organization of the spaces.
Certainly later than the original core are: the entrance corridor, adapted to a cistern in the medieval period, some rooms possibly identifiable as tabernae, and the latrine. The latter, preceded by a small antechamber with a barrel vault and remains of the ablution basin, was likely covered by a semi-dome and featured wall paintings, of which only a few traces remain today. Poorly preserved is also the floor decoration made of a black and white tessellated mosaic depicting two swimming dolphins and a fantastic marine animal.
Lighting was provided by the five windows opening on the semicircular wall. Along the perimeter of the semicircle runs the water drainage channel, continuously supplied by the cistern through underground conduits, above which were stone or marble seats with holes.
Originally, the entrance to the thermal building opened directly onto the vestibule, where the figurative mosaic made of black and white tesserae is preserved, depicting a nereid sitting on the tail of a young triton, surrounded by two cupids and dolphins, as well as traces of the dado and the wall cladding with marble slabs.
Used as a changing room (apodyterion) was a room that initially communicated with the vestibule through an entrance later sealed off. There were several routes users could choose depending on their preferences or therapeutic needs.
The main route included various stops in four rooms heated at different temperatures, then a stay in the apsidal calidarium, with a labrum for ablutions and the tub (alveus) for the hot bath, and finally access through a passage to the frigidarium with two basins for cold baths and a floor mosaic with black figures on a white background depicting fantastic animals, ridden or followed by anthropomorphic figures and dolphins at the corners.
The partial collapse of the pavements and the fall of the wall coverings exposed the structural elements related to the production of heat – the side furnaces (praefurnia) with service rooms – and its diffusion – the cavities under the floors (hypocaust and suspensurae) and along the walls. These rooms, according to the scheme known from Vitruvius, are oriented southwest, so as to better take advantage of the heat and sunlight during the afternoon hours.
