Millions of tourists visit the Colosseum and Sistine Chapel each year, but only a tiny fraction of those masses manage to get inside the gilded halls of Rome’s most exclusive location: the Colonna Palace.

The private home-museum hides in plain sight, spread out in four wings over an entire block in the city center. Its owners cling to their cloistered ways, keeping the baroque palace’s paintings, sculptures, busts, tapestries and 76-meter (249-foot) Great Hall far from most prying eyes. Doors open to small groups – 10 people at a time, guided by art historians for a few hours on Friday and Saturday mornings.

The family’s sitting prince, Don Prospero Colonna, still resides there, and he grants infrequent approval to hold events. Those have included the release of Pope John Paul II’s book in 2005, and a Metropolitan Museum of Art exhibition of Catholic fashion in 2018. Both marked rare instances of journalists gaining admission.

Since the 12th century, the palace has belonged to the Colonnas, part of the “black nobility” — the name for Roman families who remained loyal to the Pope and the Papal State when the Italian army took the city in 1870 to create a unified nation. They hung black banners outside their palaces to show they were in mourning while, within their walls, they held fast to their masterpieces.

The Colonnas for two centuries have had a sort of trust guaranteeing the palace's precious artworks forever remain there. Princess Isabella Colonna is credited with saving the family treasures. She fled Rome when the Nazis invaded, but not before ordering all artworks be “crammed into a wing of the building whose entrances were then walled up,” Cecchini said. The soldiers failed to find them.

Today, the interior betrays a past of power and privilege. Oddone Colonna became Pope Martin V in 1417 and made it the papal residence for a decade; his portrait graces the so-called Throne Room. The Great Hall’s frescoed ceiling depicts the exploits of another Colonna forebear, Commander Marcantonio, who won a 16th century naval battle that proved a watershed for the future of Europe.

With Princess Isabella’s blessing, the Great Hall – with its masterpieces set amid marble columns and glittering chandeliers — became the set for the final scene in the 1952 classic “Roman Holiday.” Playing a beloved princess herself, Audrey Hepburn addressed the foreign press corps and fielded a question: which city on her extended European tour had she most enjoyed? After some diplomatic equivocation, she stopped short.

“Rome,” she said firmly. “By all means, Rome. I will cherish my visit here in memory as long as I live.”

AP video by Silvia Stellacci, Paolo Santalucia

AP Production: Tricia Thomas