The Catacombs of St Domitilla, a massive underground maze of tombs in Rome, have been caked in grime, dust, and black oil lamp deposits since the days of the Roman Empire. Thanks to a new restoration project, archaeologists can now study some of its stunning artworks that haven't been seen for centuries, as well as some graffiti from the man who first rediscovered the catacombs.
The catacombs were recently restored using laser and scanning technology commissioned by the Vatican’s Pontifical Commission of Sacred Archaeology, the Associated Press (AP) reports. Using more conventional methods, this process could have taken years and risked damaging the artwork's fragile paint. So far, just a few rooms have been worked on, but there are dozens more to renovate within this vast underground warren of crypts.
“When we started work, you couldn’t see anything – it was totally black. Different wavelengths and chromatic selection enabled us to burn away the black disfiguration without touching the colors beneath,” Barbara Mazzei, who was in charge of the project, told The Telegraph. “Until recently, we weren’t able to carry out this sort of restoration – if we had done it manually we would have risked destroying the frescoes.”
The Domitilla Catacombs are one of Rome’s oldest underground burial networks, used from the 2nd century CE right up until the 9th century CE, when it was abandoned. In total, it houses the remains of 150,000 people, buried across 17 kilometers (10.5 miles) of channels and rooms over four different levels. These restorations took place in the larger isolated rooms, likely the final resting place for wealthy families and the elite.

Along with many illustrations of everyday life, the restoration has also revealed a number of vibrant frescoes and murals depicting both early Christian artworks and even pagan mythology. One importance of the catacomb artworks is that they capture a crucial turning point in Rome's conversion from Paganism to Christianity.
"These works show the difficult path the Romans walked on the way to their new faith," Monsignor Giovanni Carru, of the Pontifical Commission of Sacred Art, told the AP.
The catacombs were rediscovered in the 16th century by Antonio Bosio, an amateur archeologists who discovered numerous catacombs. After finding these, he scrawled his name all over the frescoes using a stick of charcoal, as you can see from the big black inscription of "BOSIO" in the photograph above (top image).
If you ever find yourself in Rome, it’s also one of the city's only underground Basilicas open to the public, although these newly restored areas won’t be open for a few months.