The Baths of Mithras (excavated in 1939-1940) were built in the Hadrianic period (opus latericium, c. 125 AD) and modified in the early-Severan period (c. 200 AD) 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 (dressing room) or vestibule. Behind that are large halls (F-G), the function of which is not clear. Room E, with niches and a basin in the west part, was a frigidarium (cold bath). 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 in this room. This was a transitional room, a tepidarium (lukewarm room). Room B also did not receive water. The walls and floor were heated. It was a sudatorium (sweating room), later extended with an apse containing a basin. The southernmost room (A) was a caldarium (hot bath), 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. In the room 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 underground service area is preserved very well. It contains several furnaces. In the underground area a statue of Vulcanus was found in a niche, apparently a fountain, in which the statue clearly does not belong.

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.

In the north part of the building, to the west of room G, is one of the staircases leading to the service area. It leads to a mithraeum that was installed in the late second or early third century (opus vittatum). 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 underground fullery.

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