This month, Rome opened a restored chamber beneath the Baths of Trajan to the public, who can view the world's largest wall mosaic and a fresco showing an unidentified city.
Here's what to know
For the first time, visitors entering the renovated underground gallery will be able to view the Great Mosaic beside the so-called Painted City fresco, Popular Mechanics reported.
Set on the Oppian Hill near the Colosseum, the two works were found in the 1990s below the Baths of Trajan. When the complex was finished in 109 C.E., it was the largest bath complex in the world.
Apollodorus of Damascus designed the baths for Emperor Trajan, yet specialists think both artworks were already old by then. Because Emperor Nero's Domus Aurea was begun around 65 C.E. and remained unfinished when Nero died in 68 C.E., some researchers suspect the fresco and mosaic may originally have belonged to that palace complex.
In roughly 107 square feet, the fresco shows a walled maritime city from above, rendered mostly in blue and terracotta, with towers, buildings, a theater, a temple, and public squares.
At 33 feet tall and 52 feet wide, the mosaic combines architectural imagery with figures in human scenes, including a poet wearing a laurel crown.
"We don't know what city [they refer] to, but it must have been a particularly well-known one," Claudio Parisi Presicce, Rome's cultural superintendent, told the Associated Press.
More background
At the unveiling, Rome Mayor Roberto Gualtieri said, "They are truly unique in the world, both from the point of view of artistic beauty and the historic and documental importance," per the AP.
An above-ground exedra, a semicircular wall thought to have functioned as a library, will also be open to visitors.
Per London's The Times, Gualtieri said, "The niches in the wall appear to have held books and documents."
What's being done?
City officials handled access cautiously, using September trials in which only 15 people were admitted at a time.
Those tests were meant to gauge how the long-buried artworks would react to more visitors and to environmental changes after so much time underground.
Presicce said the conservation work made the images easier to see, removed deposits from the surfaces, and strengthened the grouting to keep the pieces secure.
The find is still being studied.
Francesco Pacetti, an archaeologist working on the project, told The Times, "We think it's the biggest wall mosaic ever found in the Roman world, and we are still digging to find where it stops."
Where can I learn more?
Rome's underground gallery is just one of many archaeological discoveries in Rome and across Italy. Here are some more stories on finds ranging from villas and tombs near the capital to sanctuaries and necropolises uncovered during modern work.