The Nahmad family’s rise to prominence dates from its roots in Aleppo, Syria, where the family’s patriarch, also named Hillel, was a successful banker in the middle of the last century.

He had three sons, David, Ezra and Giuseppe; Giuseppe died last year in London.

David Nahmad, whose son Hillel ran the New York gallery, has been described as a risk-taker in both business and life. In Monte Carlo, he won the World Championship of Backgammon in 1996.

Over the years the family has amassed an estimated 300 Picassos worth $900 million, and about 4,500 other works by artists including Monet and Miró, many secreted in a duty-free warehouse near the Geneva airport. It is a treasure that Forbes estimated to be worth over $3 billion. Before this week, Hillel Nahmad’s gallery was a cynosure of refinement and wealth, with masters like Wassily Kandinsky and Francis Bacon on the walls.

With an entrance at Madison Avenue and 76th Street, the gallery’s connection with the Carlyle, itself synonymous with privilege, added to its prestige. The gallery has been at the Carlyle since at least the late 1990s.

However, even before the F.B.I. raid at 7:30 a.m. on Tuesday, the gallery’s windows were covered with brown paper, which is unusual since the spring art season is just kicking into high gear.

A sign on the door said, “We are closed for renovation, please ring the bell or call.”

A man who answered the phone at that number declined to speak to a reporter.