On a field next to the bullring, a house appeared which, because of some of the peculiarities that we will describe and the ancient sculptural findings of the bullring, was called the House of the Mithraeum. This is yet another house built at the end of the 1st century and the beginning of the 2nd century AC outside the city walls, without any restrictions to its growth. Its size and the decoration of some of its rooms undoubtedly show that its owners were people of Hellenistic culture who were important within the society of Mérida.

The whole building is set up around three courtyards. You enter the first one through a stairway and you arrive onto a tetra style atrium with a pond to collect water, the impluvium. It seems that this area, like other areas in the house, had a second floor because of the steps that are still preserved. Several rooms come out onto this atrium, built like other ones in the house: a masonry base and the rest of the wall in rammed earth. The walls were plastered and decorated with paintings.

One of these rooms preserves the mosaic of the Cosmos. It represents a colourful and realistic mixed group of human figures that represent the different elements of the known universe, going from terrestrial and marine elements until celestial elements, but they all revolve around the essential figure of Eternity (Aeternitas).