The Baths of the Swimmer were partly investigated during the 1938-1942 excavations. A further, stratigraphic excavation took place in the years 1966-1975, directed by Andrea Carandini.
The baths were built in the years 89-90 AD, during the reign of Domitian (opus reticulatum and latericium). A major rebuilding took place during the reign of Hadrian and Antoninus Pius. Minor modifications could be dated to the period of Marcus Aurelius and the Severan Emperors. The last signs of life in the building have been dated to c. 230-250 AD. The building was then plundered, and used as a rubbish dump.
Plan of the building (M. Medri). North is to the left.
In the centre of the west part is vestibule 1. Through room 10b the apsidal room 14b was reached, probably an unctorium, i.e. the room where the body was oiled before people went to the palaestra (27). Room 10b also led to a frigidarium (cold bath; 10a), with an apsidal basin adorned with rectangular and semicircular niches (9). In room 10a is a black-and-white mosaic with the depiction of a city wall and a swimming man. Rooms 13a and 18 were tepidaria (lukewarm rooms). In room 18 fragments were found of the stucco decoration of the ceiling (mythological figures). Room 20 was a laconicum (sweating room), rooms 19a and 19c caldaria (hot baths), with basins.
The service rooms are in the north-east part of the building, arranged around an area without a roof (25). Ovens that heated the air below the floors were located in rooms 13b and 19b. In the north-east corner is a cistern (room 26), consisting of several compartments, and two storeys high.