Mithraism is a mystic religion and it was forbidden to write about it. It originates from Persia and was brought here by Roman officials and soldiers. Religious rites could be attended only by men since the religion was secret.

In the western part of the Roman Po-etovio, on Zgornji Breg, there was the largest Mithras Shrine placed in a dense residential quarter of the town. It was discovered by Viktor Skrabar and PhD Mihovil AbramiE in 1913. The Shrine is conserved under a protected building which was already the following year repaired by the museum association with voluntary contributions. In the shrine, built in the middle of the 3rd century, dominate the altars with dedications from the soldiers of Legio XIII Gemina and V Macedonia, under the command of Flavius Aper. The shrine is tripartite in the longitude and has a sunk medium part. On the wall, opposite the entrance there is a fresco - a copy of the altar relief from the Mithras Shrine in Osterburken.