Three tiny rooms were built against the east facade of the Barracks of the Fire Brigade: two to the south of the main entrance to the building (3.20 x 1.90 and 2.28 x 1.90), one to the north (3.52 x 1.95). There are a few remains of brick walls. On the floor are black-and-white mosaics, possibly from the early third century. The depiction of chalices has suggested to some that these were bars, apparently used by the vigiles, the fire-fighters.

The floor of the room to the north of the entrance has a white background. In the centre is a black chalice, surrounded by two black frames, to be looked at from the south. Between the frames are two black rectangles, one of which is solid.

The floor of the northernmost of the two southern rooms has a black background. In the centre is a white chalice in a white frame, to be looked at from the north. In the south-west corner is a white frame with an inscription that must be read from the east:

The floor of the southernmost room has a black background. In the south-west corner is a white tabula ansata with a Greek inscription that must be read from the east:

In the facade of the Barracks of the Fire Brigade, above the mosaics, are traces of roofs: beamholes and cement for fastening roof tiles. Hermansen has suggested that the bars were held as a concession by the vigilis or ex-vigilis Proculus. This is hard to understand, because the vigiles came from Rome for periods of four months. Others have suggested that he actually made the mosaics, but the expression miles cohortis contradicts this idea.

It is most unlikely that the rooms were bars. They are far too small, but above all it is curious, to say the least, that permission was given for the installation of bars flanking the main entrance, facing the large shrine of the Imperial cult in the barracks. Most likely the rooms served a religious purpose.