A judge has ordered a former curator who the British Museum says stole hundreds of artifacts to return any gems or jewelry from the institution that are in his possession.

The museum claims that the former curator, Peter Higgs, who once ran the museum’s Greek and Roman antiquities department, stole or damaged over 1,800 artifacts from its collections and sold hundreds of those items on eBay, according to court documents.

Officials also want Mr. Higgs to explain the whereabouts of other artifacts that they says the former curator sold online. The court documents state that Mr. Higgs disputes the accusations against him.

At a High Court hearing in London, the presiding judge, Heather Williams, ordered Mr. Higgs to return any items within four weeks. Judge Williams also ordered PayPal, the online payments company, to disclose data relating to Mr. Higgs’s eBay accounts, including his transaction history.

The missing museum items include engraved gems and jewelry, some of which are thousands of years old.

On Tuesday, Mr. Higgs and his family did not respond to emails and social media messages from The Times. In court papers, the museum’s lawyers said the curator was “suffering from severe mental strain” and was “unable to respond effectively to the proceedings.”

Since the museum announced the thefts in August, it has only recovered around 350 of the missing artifacts.

The London police are investigating, but a spokeswoman for the force said in an email on Wednesday that it had not charged anyone in connection with the missing artifacts.

The museum said in court documents that it had “compelling evidence” that between 2009 and 2018, Mr. Higgs “abused his position of trust within the museum” to take artifacts, including items that the museum hadn’t fully registered in its catalog. Mr. Higgs then sold many of them on eBay to at least 45 different buyers, the museum says. Those buyers allegedly include people from the United States and Denmark.

In the filing, the museum also accuses the former curator of attempting to cover up the thefts by altering the museum’s digital catalog, including changing descriptions of missing items.

Although British newspapers had long reported that Mr. Higgs was the curator at the center of the scandal, Tuesday’s hearing was the first time that the museum had named him.

When the museum fired Mr. Higgs for gross misconduct in July, he had been working there for over 30 years. In 2021, the museum promoted Mr. Higgs to acting keeper of its Greek and Roman department — an important position overseeing some of the museum’s most treasured artifacts, including the disputed Parthenon Marbles.

Mr. Higgs curated several blockbuster British Museum shows, including a 2016 exhibition on Sicilian history. Another of his exhibitions, “Ancient Greeks: Athletes Warriors and Heroes,” toured to Australia and China.

The museum’s legal team told the court that the institution was trying to compel Mr. Higgs to give details about the items it says he stole because there was a risk they could soon “become irrecoverable.”

“So long as the items are at large, recovery of the stolen items becomes more difficult as items are sold and resold, potentially across borders,” the museum’s lawyers told the court. “The sooner the museum is able to contact other buyers,” it adds, “the more likely it is that further property will be recovered.”