The largest ancient wall mosaic in the city of Rome, and probably the largest in the Roman world, has been revealed to the public for the first time with the opening of the new Museum of the Baths of Trajan. Known as the “Muse and the Philosopher,” the mosaic adorns a huge wall on the Oppian Hill overlooking the Colosseum. It is 10 meters high and 16 meters wide (33 x 52.5 feet) and depicts an architectural structure believed to be a two-tiered theatrical background (the scaenae frons) with columns, walls that looks decorated with inlaid marble, statues and figures including Muses, a bearded philosopher and Apollo himself.

The Baths of Trajan was an enormous bath complex built by the Emperor Trajan in 109 A.D. Covering an area of 80,000 square meters (15 acres), the complex was the first Roman bath to create an outdoor park for people to use, along with the bathing and athletic facilities that were customary. It used the remains of Nero’s opulent Domus Aurea palace as its foundation. The mosaic wall dates to the 1st century and is not believed to have part of the Domus Aurea, but many of its tesserae are missing, likely taken for use during the construction of the baths. Most of the Great Mosaic was discovered in 2011, but recent excavations have uncovered a new section that shows a view of maritime villas on a Roman port in absolutely incredibly detail. It’s not clear whether this is a real port being depicted or an ideal one.

The excavation of the mosaic is not complete yet, but cultural heritage authorities decided to open the underground gallery and exedra of the Baths of Trajan to the public for the first time this weekend. For now, admittance will be limited to a few days a week and only to small groups of ticketed people. Tours will be guided and free and charge, but must be reserved ahead of time.

Also in the same structure is the largest wall fresco ever discovered from the Roman era. Dubbed the Painted City, it presents a bird’s eye view of a city encircled by walls and towers. The buildings inside are painted in perspective.

Complete with high walls, towers, gates, a theatre and golden statues, the city is surrounded by the sea. Bustling neighbourhoods are painted in such detail that the windows of houses are clearly visible. “If it did exist, it was extremely important,” Claudio Parisi Presicce, Rome’s heritage chief, said.

It was first unearthed in 1997 and has now been restored. A walkway connecting to the spaces has been built above the room so people can see the works up high. The museum also houses huge lead pipes (fistulae) that supplied water to the Baths of Trajan.