Lovers of Roman-era art and archaeology can thank the Vatican's parking problem for the discovery of one of the ancient world's best preserved necropolises - right inside the tiny city-state's walls.

The necropolis was opened three years after it was unearthed by workers who were breaking ground for a new garage to ease the Vatican's dearth of parking space.

"We found the kind of things that have usually been lost in past excavations in Rome," said Giandomenico Spinola, director of the excavation and restoration works.