Mussolini lived at Villa Torlonia in 1925-1943 with his wife and children, delighting in tennis games and horseback rides on the grounds that surround the house, built by one of Rome's aristocratic families.
"When the winds of war started blowing, he ordered the construction of the bunker," said Eugenio La Rocca, superintendent for Rome's monuments.
Two underground structures, built in great secrecy, cover more than 2,000 square feet and include an anti-gas chamber with air ducts and showers for decontamination, all protected by a double set of airtight doors.
Mussolini dug the bunker 23 feet deep, burying a 10-foot thick concrete box with bare cylindrical corridors and multiple escape routes.
While restoring the chamber, archeologists discovered it was built over a second-century Christian tomb, where they found three bodies. The area was a common burial ground in Roman times, housing mainly the sprawling underground corridors of one of six Jewish catacombs in the city.