“Whenever you dig a hole,” Mr. Martini said, “centuries of history come out.”

Ask the Faggiano family. Mr. Faggiano planned to run the trattoria on the ground floor and live upstairs with his wife and youngest son. Before they started digging, Mr. Faggiano’s oldest son, Marco, was studying film in Rome. His second son, Andrea, had left home to attend college. The building was seemingly modernized, with clean white walls and a new heating system.

“I said, ‘Come, I need your help, and it will only be a week,’ ” Mr. Faggiano recalled.

But one week quickly passed, as father and sons discovered a false floor that led down to another floor of medieval stone, which led to a tomb of the Messapians, who lived in the region centuries before the birth of Jesus. Soon, the family discovered a chamber used to store grain by the ancient Romans, and the basement of a Franciscan convent where nuns had once prepared the bodies of the dead.

If this history only later became clear, what was immediately obvious was that finding the pipe would be a much bigger project than Mr. Faggiano had anticipated. He did not initially tell his wife about the extent of the work, possibly because he was tying a rope around the chest of his youngest son, Davide, then 12, and lowering him to dig in small, darkened openings.