The earliest known icons of the apostles Peter and Paul have been discovered in a catacomb under an eight-storey modern office building in a working-class neighbourhood of Rome, Vatican officials said Tuesday.

The images, which date from the second half of the 4th century, are 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.

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The earliest known icons of the apostles Peter and Paul have been discovered in a catacomb located under a modern office building in a residential neighbourhood of Rome. ((Pier Paolo Cito/Associated Press))

The paintings adorn what is believed to be the tomb of a Roman noblewoman in the Santa Tecla catacomb. They represent some of the earliest evidence of devotion to the apostles in early Christianity, Vatican officials said in opening 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, Pope Benedict XVI also announced that tests on bone fragments long attributed to Paul "seemed to confirm" that they did indeed belong to the Roman Catholic saint.

On Tuesday, Vatican archeologists announced that the image of Paul discovered last year was 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.

'First images of apostles'

"These are the first images of the apostles," said Fabrizio Bisconti, the superintendent of archeology for the catacombs, which are maintained by the Vatican's Pontifical Commission of Sacred Archeology.

The Vatican office oversaw and paid for the two-year, 60,000-euro restoration effort, which for the first time used lasers to restore frescoes and paintings in catacombs. The damp, musty air of underground catacombs makes preservation of paintings particularly difficult and restoration problematic.

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A spotlight illuminates the icon of the Apostle John discovered with other paintings in a Roman catacomb. The paintings adorn what is believed to be the tomb of a Roman noblewoman and represent some of the earliest evidence of devotion to the apostles in Christianity. ((Pier Paolo Cito/Associated Press))

In this case, the small burial chamber at the end of the catacomb was completely encased in centimetres 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.