The Mithraeum of the Footprint was installed in a Hadrianic hall, between rows of piers of opus latericium and opus vittatum. The shrine had three naves. In the room to the east of the shrine are some basins and a well. In the west wall of this room is the main entrance of the shrine, on the east side of the central nave (w. 0.80).

Walls of opus vittatum were built between the piers on the right side of the central nave. Small benches, 0.40 high and 0.25 deep, were set against this wall, and against and between the piers on the left side of the central nave. There are no traces of podia. There could have been a podium in the left nave, but not in the right one, in view of the height of the vittatum walls behind the bench, which would have been in front of the podium. In the central part of the vertical side of each bench is a small niche (w. 0.42, h. 0.35, d. 0.30 and 0.60). In the niche on the right side chicken-bones were found.

On the floor between the benches is a simple black-and-white mosaic, with a few yellow and pink tesserae. It is divided into two equal compartments by black bands. In the part near the entrance are two depictions: a snake (1.00) and the imprint of a foot (0.25). Below the mosaic is an older floor, also with the imprint of a foot, in brick. This is the foot of Mithras, on which the initiates placed their own feet. Foot-imprints are also documented in the cult of Serapis. The Temple of Serapis (III,XVII,4) is close to this mithraeum.

In the rear part of the shrine, behind the central nave, is a large, irregular niche of small tufa stones (d. 2.00). It is decorated with plaster, with a yellow background. In the niche is a stepped altar. On the first level is a geometric black-and-white mosaic. The second level is decorated with marble. In the centre of the third level, set against the back wall, is a masonry base. In front of the niche a travertine and a marble base are standing against the lateral walls (0.30 x 0.32, h. 0.60, and 0.30 x 0.27, h. 0.50). These probably carried statuettes of Cautes and Cautopates. Mithras is often associated with Sol, and in the masonry of the altar in the niche a coin was found of Valerianus (253-259 AD) with a bust of Sol on the reverse.

A few treads lead from the central nave to the rear part of the right nave, which is a small room with a curved niche in the back wall.

In the altar the following inscription was reused:

PR(o) SAL(ute) AVGG(ustorum duorum) S(oli) I(nvicto) M(ithrae) FLORIVS HERMADIO SACERDOS S(ua) P(ecunia) F(ecit)

For the well-being of the Emperors, To Sol invincible Mithras, Florius Hermadio, priest, made it at own cost.

The following objects were found:
- A marble altar (0.30 x 0.34, h. 1.00). In the back is a curved hollow space, perhaps for a small bust.
- Fragments of a marble relief, presumably of Mithras killing the bull. Two flanking figures have been preserved: Sol and Luna. The rays of Sol were painted red.
- A round, marble basin (diam. 0.60, h. 0.25) with an inscription on the edge:

[--- IN]VICTO MITHRAE D(onum) D(edit) M(arcus) VMBILIVS CRITON CVM PYLADEN VIL[ICO ---]

... to invincible Mithras donated Marcus Umbilius Criton, with Pylades, caretaker ...

It seems significant that in the nearby Temple of Serapis an inscription from 200 AD mentions a son of Marcus Umbilius Maximinus, in 192 AD patronus of the corpus lenunculariorum tabulariorum auxiliariorum Ostiensium, a guild of auxiliary ships in the harbour.
- A dedication by Hermes, slave of Marcus Iulius Eunicus:

SILVANO SANCTO SACRVM HERMES M(arci) IVLI EVNICI

Dedicated to sacred Silvanus. Hermes, (slave of) Marcus Iulius Eunicus.

The shrine was built in the second half of the second or the early third century AD. Modifications have been dated to the second half of the third century.