The House of the Dog Monnus (Caseggiato del Cane Monnus) is on the east side of the Via dei Magazzini Repubblicani, and the building consists of six sections, or possibly rooms, in sequence from the Decumanus to the end of Via dei Magazzini Repubblicani. The structure dates from the Republican era and it had a portico of volcanic tuff (tufa) piers, a construction material common to that period. Portions of the tuff piers can be seen among the remains of the building.
Since this area between the Decumanus Maximus and the Tiber River had been set aside for public buildings, as indicated by the Cippi of Caninius, this building may have been a public warehouse or other similar structure. Construction in opus latericium indicates renovation during the Trajanic period, and there is evidence of modifications made in later time periods. No evidence of its actual function, however, in either the Republican era or at later times is known.
The most interesting feature of the building is the black and white mosaic that has been dated to the early third century AD. The Cane Monnus mosaic is a fairly large floor mosaic that covers the pavement of three or four rooms in the north part of the house. As a whole, the Cane Monnus mosaic lies in an "L" shaped pattern with a mosaic scene that appears to show a unified theme extending across three of the rooms facing the Via dei Magazzini Repubblicani.
Two separate, but related, themes are in the parts of the mosaic that are at the far south end and that are in the room east of the far north end room. The entirety of the mosaic, however, conveys a common Ostian theme of marine mythology and the richness of the bounty of the ocean.
One exception to the maritime theme is the image of a dog in the far northwest corner of the mosaic. Near the dog is the name Monnus that presumably refers to the dog, and it is this image that gives the building its modern name.
The main scene of the mosaic is that of a Nereid, a sea nymph, riding a mythical sea-lion. The Nereid looks over her left shoulder with a distressed expression as a nude young man, who is leading a sea-horse with the reins in his hands, reaches out in pursuit of the sea nymph.
The story of the mosaic, recognizable to any visitor to Ostia, a city so dependent on the vast sea beyond its shore, is the myth of Amphitrite and Poseidon.
The sea nymph Amphitrite was one of the fifty lovely daughters of Nereus, the Old Man of the Sea, and his wife Doris. Poseidon, ruler of the sea, saw Amphitrite dancing and he fell in love with her. He tried to pursue her, but she fled from him and hid. This is the scene portrayed in the mosaic.
Eventually, Poseidon sent a dolphin named Delphineus to plead for him with Amphitrite, and at last, the dolphin was successful. Amphitrite agreed to marry Poseidon, and Amphitrite became the Queen of the Sea.
Any similarities with The Little Mermaid of Hans Christian Andersen or Walt Disney Productions are purely coincidental!
The harmony of this union is represented in the panel of the mosaic to the south (right). Real, not mythical, sea creatures are represented in precise detail that makes them easily identifiable, even to us today. Three marine species are depicted: an octopus, a dolphin and an electric ray (torpedo ocellata).
The electric ray, or torpedo fish, is recognized by the five dark spots on its back, and it was well known to the Romans, although it was not used as a food source. Instead, the Greeks and the Romans knew that the torpedo fish could deliver a strong electric shock of up to 200 volts. This electrogenic property led the ancient Greeks and Romans to use it in medicine.
The Roman physician Scribonius Largus, in his Compositiones, written about 50 AD, recommended that chronic headaches be treated by the application of a live torpedo to the affected area. As a result, Scribonius Largus is credited with being the first to apply this early form of electroanalgesia to manage both headache and gout.
Two of the other sea creatures shown in the mosaic also were harvested by the Romans for the commercial value. The octopus could be prepared for food, but the ink from the octopus was extracted for medicinal purposes and for the production of writing ink. The snapper fish (chrysophrys aurata) recognizable by its oval body and bristly dorsal fin, was a common entree at the Roman dinner table, just as it is today.
The complex mosaic of the House of the Dog Monnus is worthy of further analysis. Yet, the mosaic is currently in need of restoration. It has been covered with a protective cloth as well as an overlayer of soil and grass. It is our hope that this beautiful and enchanting work will soon be returned to public view.