The owners of the kosher restaurant in Rome's Jewish Ghetto - a historic quarter in the centre of the city - were surprised when Zuckerberg and Priscilla Chan walked away without leaving a gratuity.

Their bill came to $32 (about R267) after a lunch consisting of deep-fried artichokes - a Roman Jewish speciality - fried pumpkin flowers and ravioli stuffed with sea bass and artichokes.

Instead of wine or beer, they opted for a bottle of water and a pot of tea.

Waiters at Nonna Betta, which specialises in Roman Jewish cuisine, were amazed by Zuckerberg's parsimony, not just because of his huge wealth but because of Americans' reputation for tipping generously, as is expected of them at home.

It was not a case of not enjoying the meal, said the owner of the restaurant.

"I asked him 'how was it?' and he said 'very good'," the owner, identified only as Umberto, told Corriere della Sera newspaper.

The couple's honeymoon was a closely guarded secret until a Polish tourist spotted them in the Sistine Chapel, snapped a blurry photograph, and posted it on Twitter - Facebook's social network rival.

Zuckerberg, 28, married his long-time girlfriend on May 19.