The mithraeum near the Roman Gate was excavated in 1919. It was probably built in the third century. The room was connected with the two cult rooms that together have been called Shrine II,II,4: there were doors between the mithraeum, a large cult room to the west, and a small cult room to the south. The door in the back wall (the south wall) of the mithraeum was blocked with opus vittatum. Perhaps this was done when the mithraeum was installed. The other door was either not blocked, or its blocking has disappeared.

The shrine measures 14.96 x 5.82. The usual podia line the two long walls. On these the men who had been initiated in the cult would lie down during celebrations. In the south part are the foundations of an altar. In the north part of the corridor is a small, marble basin (0.50 x 0.50). Around the basin part of the marble decoration of the floor, walls and podia has been preserved. The room has been identified as a mithraeum solely on the basis of the architecture.