Rome Opens Museum Built Around Largest Surviving Roman Wall Mosaic

The largest surviving wall mosaic in the Roman world is now on public view. The city of Rome has opened the Museo delle Terme di Traiano, or Museum of the Baths of Trajan, a 230-foot (70-meter) underground gallery on the Oppian Hill directly across from the Colosseum, where the monumental mosaic sits in situ alongside a rare fresco of a painted city.

The Oppian Hill was a densely constructed neighborhood 2,000 years ago; today it is a sunny park where immense pieces of the huge public Baths of Trajan, inaugurated in 109 CE, still protrude from the earth. When Emperor Trajan leveled the space to build a platform for his Baths, a series of buildings was buried. Archaeologists brought them to light in digs between 1997 and 1999. The hill has already produced some of archaeology's wonders: underneath the Baths, the richly decorated rooms of Emperor Nero's Domus Aurea, or "Golden House," are open to visitors through an immersive experience.

The new museum's name is slightly misleading. The only objects on display that pertain to the Baths themselves are eight huge lead pipes, cast with the words "THERM TRAIANI" in relief, astonishing for their size and their survival. They sit in an irregular ancient room to the left of the entrance. A small bookshop occupies a room to the right. Almost the whole length of the ancient vaulted gallery is given over to two unique works of art that have no clear relationship to each other and no comparable examples elsewhere in the Roman Mediterranean.

Below the floor level of the gallery, archaeologists discovered a large-scale mosaic covering two sides of a hall of gigantic dimensions: roughly 10 by 15 meters (~33 by 49 feet) with walls an astonishing 12 meters (~39 feet) tall. The dig has not yet reached the original floor, but what is already visible is extraordinary. Only about 20% of the mosaic survives, with traces on the side wall, and it lies roughly nine meters (~29 feet) below the modern walkway crossing the space. The walls were perhaps part of a nymphaeum, or fountain room, with a central niche that once contained a statue.

The mosaic's upper part draws from ancient fresco, with illusionistic architecture: thin columns with elaborate capitals and Dionysian symbols support platforms on two levels like an ancient stage, a scenae frons. Set into these spaces are two types of figures — imitation statues, like the centaur near the upper part of the mosaic, and a full-colored series of portraits of striking psychological intensity. Two of these faces, the first found by archaeologists digging downward, gave the work its name: the "Mosaic of the Muse and the Philosopher." Other faces were later found grouped toward the lower register.

The room's function remains uncertain. It dates from after the Great Fire of Nero in 64 CE to the end of Emperor Domitian's reign in 96 CE, and it was likely a large imperial reception room, an oecus. The regularity of the missing sections suggests that blue glass mosaic tiles were stripped out and reused.

At the far end of the Trajanic gallery lies a second discovery: a large fragment of an unusual fresco, also painted after 64 CE and before Domitian's death. It decorated the exterior of a different building that Trajan's engineers leveled to build the Baths. The fresco shows a painted city in a bird's-eye view, rich in detail: turreted walls, a main gateway, an Odeon or roofed theater for poetry readings, a temple, a four-sided portico, residential buildings, and a heavily fortified harbor. Scholars do not agree on its subject. It might be an imaginary city, a Near Eastern city on the Mediterranean, or even Londinium.

Rome Mayor Roberto Gualtieri, at the inaugural press conference, emphasized the discovery's significance for the city. "With this intervention, we are returning a wonderful and finally accessible place to the city, recovering unique testimonies of Rome's history," Gualtieri said. "The restoration of the 'Painted City' and the 'Great Mosaic,' along with the new discoveries that emerged from the excavations, also tells the extraordinary nature of a city where every intervention on heritage can bring new fragments of history to light and enrich the knowledge of our past."

With the excavation not yet reaching the hall's original floor, further finds below the mosaic remain a real possibility as work on the Oppian Hill continues.