An 18-carat gold toilet entitled "America" was stolen from Blenheim Palace, England, on Saturday morning.
Italian satirical artist Maurizio Cattelan created the famous sculpture and fully functioning loo, which was first installed in New York's Guggenheim Museum in 2016.
It was part of an exhibition at the palace — a world heritage site and the birthplace of Sir Winston Churchill — that opened on Thursday.
It was Cattelan's first solo showcase in the United Kingdom, the palace said.
The burglary occurred in the early hours of the morning and police said they thought the offenders used two vehicles.
Police arrested a 66-year-old man in connection with the incident but the toilet had not been recovered.
“Due to the toilet being plumbed into the building, this has caused significant damage and flooding," Thames Valley Police detective inspector Jess Milne said.
The palace closed for the day after the incident.
The CEO of Blenheim Palace, Dominic Hare, called on people to contact the police with any information.
He said it was "a great shame an item so precious has been taken, but we still have so many fascinating treasures in the Palace and the remaining items of the exhibition to share".
"The investigation continues, but it will be business as usual from tomorrow, so visitors can continue to come and experience all we have to offer."
Critics have described the sculpture as a commentary on affluence and excess in Donald Trump's United States of America.
More than 100,000 people queued to use the functioning toilet at the Guggenheim when it was first installed, the museum said.
A curator for the Guggenheim reportedly even offered the sculpture to the Trump White House after refusing to loan a Vincent Van Gogh piece to the White House curator, according to an email released by the Washington Post.
When the toilet first went on display in 2016, Cattelan described it as a type of equaliser in an interview with The New Yorker.
"Whatever you eat, a two-hundred-dollar lunch or a two-dollar hot dog, the results are the same, toilet-wise," he said.