The Baths of Mithras (excavated in 1939-1940) were built in the Hadrianic period (opus latericium) and modified in the Severan period and in the first quarter of the fourth century (opus latericium and vittatum). To the east of the building was an arcade of eleven arches, that later became part of the baths. The main entrance to the building is on the east side and leads to room H, an apodyterium or vestibule. Behind that are large halls (F-G), the function of which is unknown. Room E, with niches and a basin in the west part, was a frigidarium. Here a mosaic of Ulysses and the Sirens was found. To the east is a small basin (I). In room D the walls and floor were heated. There is no water supply. This was a transitional room, a tepidarium. Room B also did not receive water. The walls and floor were heated. It was a sudatorium, later extended with an apse containing a basin. The southernmost room (A) was a caldarium, with two rectangular basins (a later addition).

In the south part of the ground floor of the building (to the south of room A) is a narrow corridor, to the south of which is a room for a waterwheel (w). Wear-marks are visible on the side walls, on the west wall only below the water-surface. There were various water-lifting devices here and the situation was adapted several times. A description is found below, with reconstruction drawings.

The underground service area is preserved very well. It contains several furnaces. To the east of room A is a big water-boiler. It was fed, like the basins, through various conduits. By closing sluice gates the water could be forced to specific places.

The building was decorated with two imagines clipeatae, shields with portraits. The portraits were made c. 100 AD and probably depict members of the family that had financed the baths. See also Guy de la Bédoyère's page.

In the underground area a statue of Vulcanus was found in a niche, apparently a fountain, in which the statue clearly does not belong.

In the north part of the building (room G) is a staircase leading to the service area. Here a mithraeum was installed (opus vittatum) in the late second or early third century. The cult statue of Mithras, about to kill the bull, was found in situ, and a plaster cast has been placed in the shrine. Light falls on the statue in a dramatic way, through an opening in the ceiling, as it did in antiquity. In the north-east part of the service area is a tiny fullery.

In late antiquity the building was no longer heated: tubuli were taken from the walls and furnaces were filled in. The basins of the caldarium were filled with cold water. The various basins and fountains may now have been used for baptizing: a Christian oratory was installed in room G.