BERLIN — After hundreds of years residing in a cathedral in Braunschweig, Germany, the Guelph Treasure has had a comparatively active century. The trove of medieval religious art was sold just before the stock market crash in 1929, sent to the United States and back, then split up and sold. All 82 pieces have changed hands at least twice.
Now, it is the subject of a U.S. Supreme Court case that could see 42 pieces, estimated to be worth nearly a quarter of a billion dollars, on the move again.
The dispute centers on a transaction in 1935, when a consortium of Jewish art dealers that bought the entire collection in 1929 sold those 42 pieces to a German museum. For more than a decade, descendants of those dealers have claimed that the sale was made under duress and that the price paid — the equivalent of about $20 million today — was far below value. At least one of the dealers lived in Germany, then under Nazis rule, at the time of the sale, raising the possibility that his life was under threat while the deal was being brokered, descendants of consortium members say.
The 42 pieces that were sold ended up in the Museum of Decorative Arts in Berlin. In 2014, a German arbitration commission that specializes in Nazi-looted art ruled that the museum had acquired the collection legitimately and did not need to return them.
After the families took the case to an American court, museum administrators and the German government turned to the Supreme Court, hoping it would confirm the case was outside its jurisdiction. The U.S. Solicitor General wrote an amicus brief supporting the German position, as it frequently does with cases involving foreign affairs.
The justices announced this month that they would decide whether the case could proceed and are expected to make a ruling later this year. If they allow it, a lower court will rule on the ownership issue, not the Supreme Court itself.
Nicholas M. O’Donnell, a lawyer representing the families, said they were entitled to bring their case in an American court because Nazi Germany had violated international law.
“Germany seeks to eliminate recourse for Nazi-looted art and the court will have the chance to answer this question of critical importance for Holocaust victims,” Mr. O’Donnell said.
The case has put the Prussian Cultural Heritage Foundation, which oversees Berlin museums including the Museum of Decorative Arts, in an awkward position. The foundation prides itself on its provenance research and on its active role in returning objects to their rightful owners when appropriate.
In an interview, Hermann Parzinger, the president of the foundation, was clear about the foundation’s principles. “What’s really important is how seriously we take this: We have returned thousands of books and hundreds of pieces of art — we don’t want stolen objects in our collections,” he said.
In this case, however, the foundation says the sale was not only legal, but also fair.
“There are those who say that everything that changed hands after Jan. 30, 1933, was confiscated under duress,” Mr. Parzinger said, referring to the date the Nazis came to power in Germany. “But we think that each case needs to be investigated.”
The foundation has processed about 50 restitution requests in the last two decades, according to Birgit Jöbstl, a spokeswoman for the foundation. Its own researchers had checked several thousand other works in the collections, leading to 350 objects going back to their rightful owners, she added.
Petra Winter, the director of the foundation’s provenance department, said her team of seven full-time researchers, including art historians, archaeologists and archivists, have been systematically retracing the histories of objects acquired in the Nazi period.
In the case of the Guelph Treasure, the foundation’s inquiries suggest that the pieces were in Amsterdam and out of the hands of the Nazis when the collection was sold, and that consortium’s lead negotiator brokered the deal with Berlin from there.
The foundation’s research also indicated that some of the treasure had been paid for in kind, in a bid to circumvent laws that prevented German money leaving the country: Pieces from the museum’s collection were exchanged as part of the transaction.
She said that the dealers were not able to sell the most valuable items in the collection anywhere else (a museum in Cleveland bought a smaller part at a comparable price) and were getting desperate by the time they made the sale.
“We believe that the final sale price was appropriate,” Mr. Parzinger said.
Today, the Museum of Decorative Arts has 44 pieces of the Guelph Treasure — having added two further pieces of the collection to the 42 bought in 1935 — including works made of gold, silver, ivory, glass, tin and sea lion tusk. Among the items are reliquaries with human remains reputed to be the bone fragments of saints brought back from the crusades.
Lothar Lambacher, the museum’s deputy director, said the treasure was “the highlight, the center, the heart of our medieval collection.” Referring to one piece, a delicate statuette of a church that is a masterpiece of 12th-century art, he said, “The dome reliquary is our Mona Lisa.”
The objects have stood in the same display room of Museum of Decorative Arts for the past 33 years. But a decision from the Supreme Court in favor of the families could set in motion a process that would lead to their removal.
Mr. O’Donnell, their lawyer, said: “We are grateful for the opportunity to address the Supreme Court on these important questions about holding Germany accountable for its Nazi-looted art.”