Excavations in a tunnel under the 2nd century A.D. Baths of Trajan on Rome’s Oppian Hill have unearthed a large wall mosaic depicting Apollo and the muses. The newly discovered stretch of mosaic is 33 feet wide and at least 6 feet high. An earlier excavation in 1998 found the first 20 feet of it, a male figure, apparently a philosopher, and a female figure on either side of a columned architectural structure. Archaeologists suspect the mosaic wall continues even further, perhaps as much as 30 feet down.

The tunnel pre-dates the construction of the baths in 109 A.D., but was built after the nearby Domus Aurea (Nero’s Golden House) which was completed in 64 A.D. That means we can conclusively date the mosaic to some time within that 45 year span. This kind of tunnel was called cryptoporticus, meaning hidden gallery, and was usually a subterranean support for a large building above that had an alternative use as a service corridor. This particular one was used as a powder keg during the Napoleonic occupation of Rome, and in more recent times as a tool shed for park workers.

Such an elaborate and extensive mosaic wouldn’t have been placed in a service tunnel, though, so the space must have had a more social function for the Roman élite, possibly something music related given the Apollo and muses theme.

The discovery was announced by at a press conference on Friday that was part advertising and part pitch for financial support, a common combination is these austerity budget days.

“An archaeological discovery is of extraordinary value to the city of Rome,” said Mayor Gianni Alemanno, thanking the archaeologists for uncovering the treasure of ancient Rome.

He insisted on making it accessible to public and tourists and this would require more funding for the excavations work.

“Now we must make an extra effort to find adequate financial resources to continue the work in the yard and open to the public. I hope, in this sense, the concurrence of all competent authorities to find the necessary resources,” the mayor said.

The necessary resources include an immediate infusion of 200,000 euros ($287,000) to continue the excavation and to make the gallery accessible to the public for guided tours by next October. The next step in the project requires another 480,000 euros ($690,000) to ensure that the entire cryptoportico area is fully explored and stabilized.

Giant mosaics aren’t the only treasures that have been found in the area. In 1997 a fresco of a Roman city, possibly representing an actual city, possibly an ideal one, was discovered. The rare bird’s-eye view fresco was a boon to architectural scholars as well as art historians. Another fresco depicts a vibrant scene of grape stomping. The city of Rome would love to have such a rich vein of Roman art open to tourism.