The Mithraeum of Lucretius Menander was installed in the early third century AD in an alley to the east of a Hadrianic building named after the mithraeum. It is in a part of the alley that had become part of an apartment. The rooms had then been decorated with a black-and-white geometric floor mosaic. On the walls were paintings similar to those in rooms to the west. On a grey-blue socle are horizontal yellow and red bands. Above that, on a white background, high rectangles are created by red bands with internal yellow and blue lines. In the centre of the rectangles are small paintings: birds in an landscape, birds and a basket, a little temple and trees. The plaster has been dated to the reign of Marcus Aurelius. When the mithraeum was installed, no new paintings were made.

The mithraeum was entered from the north, along a staircase which forced access from the side. Along the walls of the shrine are podia (h. 0.45), with niches in the centre of the vertical side. The western podium was reached along a few treads at the north end.

At the back of the shrine is a brick altar. The front was covered by a marble slab (0.84 x 0.47). It has a hole in the shape of the moon, behind which must have been a lamp. Below the moon is the inscription:

DEO INVICTO MITHRAE DIOCLES OB HONOREM C(ai) LVCRETI MENANDRI PATRIS D(ono) D(edit) D(edicavit)

To the invincible god Mithras, Diocles, in honour of Caius Lucretius Menander, father, donated and dedicated this gift.

This mithraeum is almost back-to-back with the mithraeum in the House of Diana. The nearness of two mithraea is exceptional: these shrines are normally spread out evenly over the city, presumably because the worshippers came from the area surrounding a shrine.