The discovery of the site, which happened entirely by chance, was followed between 1953 and 1966 by an archaeological investigation led by Dutch archaeologists M.J. Vermaseren and C.C. van Essen.
As often happened, the Mithraeum was installed within a pre-existing private house, located underneath the northern part of the church and its surrounding courtyard. Featuring an eastern quadriporticus encircling a garden, the house dates back to the late 1st century AD and underwent modifications during the 2nd century.
The space is defined by two niches symmetrically positioned on either side of the entrance and two slightly sloping benches along the longer walls, framing a central aisle leading towards the main cult niche set into the back wall. Originally, statues of the two torchbearers, Cautes and Cautopates, stood in the entrance niches.
In the main niche at the center, there was once a group sculpture of Mithras, depicted with a fluttering cloak, along with the dog and the bull; fragments of this scene remain.
The two long side walls, above the benches, are adorned with two cycles of frescoes. Based on architectural changes, these are dated to around 200 and 220 AD. The frescoes portray sacred processions, the seven grades of initiation for the mystae, and the divine banquet. On the right-hand wall, the initial section shows a group of figures dressed in red tunics preparing for the suovetaurilia (a sacrifice of a pig, sheep, and bull). Each figure is topped by an inscription—a truly unique testimony—that, drawing from Mithraic hymns, identifies the person’s degree of initiation.
On the opposite long wall, the procession of the leones continues, with each one named and identified by their initiation grade. The sequence finishes near a cave where, at a table, Mithras—wearing a red cloak and Phrygian cap—is depicted raising a toast. Next to him, Sol, with a radiant halo, holds the globe close to his side. Alongside the two gods stands a small attendant. The scene represents the banquet during which the two deities pledge mutual eternal loyalty.
