The European Union and Britain began trade negotiations on Monday.

The EU is set to ask Britain to give back ancient marble sculptures back to Greece as part of the deal.

Greece argues that the Parthenon Marbles, shipped from Athens by the British diplomat Lord Elgin more than 200 years ago, were taken unlawfully and should be returned.

The sculptures, considered one of the great works of ancient civilization, are displayed in a custom-built wing of the British Museum in London.

The Greek government told Business Insider that the marbles had been "brutally removed" by Britain.

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The European Union will ask the UK to give back to Greece a collection of ancient marble sculptures which Athens says were "brutally removed" by Britain over 200 years ago.

Greece has long argued that the Parthenon Marbles — sometimes called the Elgin Marbles — were unlawfully removed from the Parthenon temple in Athens in the early 19th century by the British diplomat Lord Elgin.

The marbles — considered among the great works of ancient civilization — are displayed at the British Museum in London in a wing custom-built to accommodate them.

The EU's negotiating mandate for talks with the UK contains a stipulation on "the return or restitution of unlawfully removed cultural objects to their countries of origin." Brussels included this clause at Greece's request.

A spokesperson for the British Museum said that the classical Greek structures were taken from the Parthenon temple lawfully and were "accessible to the 6 million global visitors the museum receives each year."

However, the Greek embassy in the UK told Business Insider that the marbles were taken "without the consent of the Greek people," and that "British claims about the legality of the acquisition has been seriously challenged by series of scholars and scientists."

They said: "Recently, the Greek Prime Minister made an appeal, on the occasion of the Bicentennial of the Greek Independence War in 1821, to reunite the Parthenon Marbles that were brutally removed from the monument in Athens.

"This appeal is addressed to all parts involved, as well as Britain, where the majority of the sculptures were transported. The demand for the Reunification of the Parthenon Sculptures is universal and it is based on the fact that the sculptures are integral parts of one of the most emblematic culture monuments in the world."

They added: "We understand the keen interest of the media regarding the long-standing issue of stolen antiquities and the different approaches to it.

"Nevertheless, it is widely acknowledged that these artefacts were removed from the monument without the consent of the Greek people who were still under the Ottoman rule and this inflicted serious damage to the Parthenon itself at the time.

"As a matter of fact, even the British claims about the legality of the acquisition has been seriously challenged by series of scholars and scientists."

A Downing Street source recently told the newspaper The Sun that the marbles were "going nowhere."

"This shows a troubling lack of seriousness about the negotiations on the EU side," the person added.

British and EU negotiators sat down for the first round of trade talks on Monday. The two sides aim to reach some sort of agreement by the end of the year, when the 11-month Brexit transition period comes to an end.

The question of which country ought to have the Parthenon Marbles is just one issue in what are set to be a bruising series of negotiations.

In a negotiating mandate published last week, Johnson's UK government set up a clash with Brussels by saying it would not sign up to EU rules — or what is known as a "level playing field" — as part of a free trade agreement.

Fishing is also set to be a difficult issue to resolve. Johnson has pledged to take full control of Britain's fishing waters as part of Brexit. The EU, however, wants European fishing boats to retain access to them.

The UK government's negotiating mandate warned that it would be walk away from talks in June and prepare for life on harsh trading terms with the EU if there had not been sufficient progress in negotiations.