This structure seems to consist of two shrines, accessible from the Decumanus through wide passages: a small room to the right, and a much larger room to the left. Both rooms have doorways leading to the adjacent mithraeum II,II,5 to the north-east, but at least one of these doors was blocked, perhaps when the mithraeum was built. The rooms were excavated in 1919.

In the small room (opus mixtum) is a geometric, black-and-white mosaic, installed c. 150 AD. In the back wall was a niche, decorated with red plaster. A doorway, now blocked with opus vittatum, to the right of the niche led to the room in which the mithraeum was installed. The large sacellum (5.20 x 14 metres; opus latericium) to the left has been dated to the mid-second century AD. The present north wall is apsidal, and made of opus vittatum from the third century AD. It probably replaces a straight north wall. A masonry base (w. 1.10, d. 0.60) for a cult statue is standing against the apsidal wall. The floor is decorated with two polychrome mosaics from the middle of the second century AD.