As often happens with construction projects here, the workers quickly made way for archaeologists who, over the space of three years, uncovered some 250 tombs of various shapes and sizes dating from a few years before Jesus Christ to the early fourth century - under the emperors Augustine through Constantine.
Walkways overlooking the dig allow visitors to view the city of the dead, dubbed a "funerary Pompei" by Vatican Museums director Franceso Buranelli at a news conference.
The archaeologists deliberately limited their restoration work to a minimum so that the sepulchers can be viewed in the state in which they were found: steles bearing Latin inscriptions, vaults lined with funerary urns still containing ashes, skeletons lying in their niches.
But they painstakingly recomposed several precious artifacts, including black and white mosaics, amphoras and, for example, the travertine head of a child, displayed in a glass case at the dig, which is under cover and walled in.
Sarcophagi belonging to well-to-do families lie alongside humble funerary urns and provide precious clues to social classes, daily life, and the religious upheaval that was rocking Rome at the time of the advent of Christianity, which was finally embraced by Constantine after suffering frequent persecution, Buranelli said.
Many graves contain objects that were placed alongside the dead.
An egg lying beside the body of a small child suggests the symbolism of hope for rebirth.
Among sarcophagi decorated with hunting scenes is the more austere tomb of a young horseman who died at age 17 that bears images of a philosopher and a woman at prayer under a tree and a bird: suggesting that the youth and his family belonged to the first generation of Christians.
The necropolis along the ancient Roman Via Triumphalis leading north out of the city turned out to be the extension of a smaller site discovered in the 1950s.
The site, which will open as the Vatican Museums mark the 500th anniversary of their establishment, may be visited by appointment Friday and Saturday mornings.
© 2006 Agence France-Presse