The earliest known icons of the Apostles Peter and Paul have been discovered in a catacomb under a modern office building in Rome.
The images, which date from the second half of the 4th century, were discovered on the ceiling of a tomb that also includes the earliest known images of the apostles John and Andrew.
They were uncovered using a new laser technique that allowed restorers to burn off centuries of thick white calcium carbonate deposits without damaging the dark colours of the original paintings underneath.
The paintings adorn what is believed to be the tomb of a Roman noblewoman in the Santa Tecla catacomb and represent some of the earliest evidence of devotion to the apostles in early Christianity, Vatican officials said in opening up the tomb to the media for the first time.
Last June, the Vatican announced the discovery of the icon of Paul - timed to coincide with the end of the Vatican's Pauline year. At the time, the pope also announced that tests on bone fragments long attributed to Paul "seemed to confirm" that they did indeed belong to the Roman Catholic saint.
Today Vatican archaeologists announced that the image of Paul discovered last year was not found in isolation, but was rather part of a square ceiling painting that also included icons of three other apostles - Peter, John and Andrew - surrounding an image of Christ as the Good Shepherd.
"These are the first images of the apostles," said Fabrizio Bisconti, the superintendent of archaeology for the catacombs, which are maintained by the Vatican's Pontifical Commission of Sacred Archaeology.
The Vatican office oversaw and paid for the two-year restoration effort, which for the first time used lasers to restore frescoes and paintings in catacombs. The damp, musty air underground makes preservation of paintings particularly difficult and restoration problematic.
In this case, the small burial chamber at the end of the catacomb was completely encased in inches of white calcium carbonate, which under previous restoration techniques would have just been scraped away by hand. That technique, though would have left a filmy layer on top so as to not damage the paintings underneath.
Using the laser, restorers were able to sear off all the layers of calcium that had been bound onto the painting because the laser beam stopped burning at the white of the calcium deposits, which when chipped off left the brilliant darker colours underneath it unscathed, said Barbara Mazzei, the chief restorer.