Catacombs.

Architecture In 1950, Life Magazine collected photos of an excavation of the catacombs beneath the Vatican City:

"Deep in the earth below the great basilica of St. Peter’s in Rome the clink of pickaxes and the scrape of shovels in the hands of workmen have been echoing dimly for 10 years. In the utmost secrecy, they have penetrated into a pagan cemetery buried for 16 centuries. Architects feared they might disturb the foundations on which rests the world’s largest church. But the workmen, with careful hands, pushed forward finally to the area where, according to a basic tenet of the Catholic Church, the bones of St. Peter were buried about A.D. 66."

The identity of those old bones remains ambiguous.