This tiny, surely privately owned, store building is on an isolated location, to the south of the Baths of the Six Columns. It was entered from the south. In front of the entrance is a large, Hadrianic brick archway. In the east wall of the central east room is a door leading to the Courtyard of Dionysus.

There are six rooms, three on either side of a wide central corridor (width 4.80). The doors of the rooms are 2.34 wide. A few thresholds have been preserved, with two pivot holes and bolt holes. One was later changed into a shop-threshold. Three buttresses composed of very large travertine blocks were set against the north wall. The thickness of the walls is 0.60, enough to carry several upper floors, but there are no remains of staircases.

The opus reticulatum has been dated to the early first century AD. In the south-east room the Mithraeum of the Seven Gates was installed.