The Mithraeum of the Animals was excavated by Carlo Ludovico Visconti in 1867. It was set against the wall surrounding the Field of the Magna Mater, in a hall with three rows of brick piers and pilasters. The shrine was entered through two openings between the piers (a third opening was blocked by a thin wall of opus latericium). Next to the altar is a secondary entrance. Podia were found only in the back part, in front of the altar (l. 4.50, w. 1.50).

The brick altar was set against the back wall (w. 2.40). In the front part are three treads. In the centre of the second tread is a rectangular niche (w. 0.50, d. 0.17). The back part is a podium, that - witness a few traces - carried a niche (d. 0.90) flanked by pilasters. The entire structure was revetted with white marble.

On the floor, between the piers and the podia, is a black-and-white mosaic. It contains a marble threshold at the point where the podia begin. There are five depictions, from south to north:
- A naked man, holding a pruning knife and some sort of shovel. A few white tesserae suggest that the latter object is perforated (or do they represent glowing coals?). A similar symbol is found in the Mithraeum of Felicissimus, where it refers to the grade Leo. It was used to carry fire. The hair of the naked man may be the lion's mane. However, in the Mithraeum of Felicissimus the knife refers to the grade Perses. Apparently this depiction is a reference to two grades of initiation.
- A cock, announcing the morning, attribute of Cautes, and a raven, the herald of Mithras and a grade of initiation (corax).
- A scorpion, that on reliefs attacks the testicles of the bull that is killed by Mithras.
- A snake with a comb, on reliefs drinking the blood of the bull.
- The head and tail of the bull, and in front of the head part of a knife (half of which is missing, as if it is in the neck of the bull).

Near the altar a head of Mithras with Phrygian cap was found (h. 0.45). In the cap are holes for metal rays, so Mithras is depicted as Sol Invictus. Furthermore a head of Sol-Helios was found, with seven holes for rays.

The shrine was built in the second half of the second century AD.