Pope Francis has decided to return three Parthenon pieces to Greece in a move that could add pressure to the U.K. government as it stands firm regarding its own collection of Parthenon marbles. The return, announced Friday, is expected to take some time to execute.

It is not the only repatriation agreement Greece has struck this year. In January, a small museum in Palermo, Sicily, decided to return its only Parthenon fragment in a loan move that Greek authorities hope will be extended indefinitely.

In announcing the decision, the Vatican termed the gesture a "donation" from Francis to His Beatitude Ieronymos II, the Orthodox Christian archbishop of Athens and all Greece, and said it was "a concrete sign of his sincere desire to follow in the ecumenical path of truth."

Greece's Culture Ministry and the Acropolis Museum welcomed the move. 

Pope Francis and Ieronymos II

Pope Francis and Archbishop Ieronymos II in Athens, Greece, December 6th, 2021. (Photo by Vatican Media/Pool/Spaziani/Mondadori Portfolio via Getty Images)

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The Vatican statement suggested the Holy See wanted to make clear that its donation was not a bilateral state-to-state return, but rather a religiously inspired donation from a pope to a primate. The intent may be to avoid a precedent that could affect other priceless holdings in the Vatican Museums.

Francis last met with Ieronymos in 2021 in Athens where he issued an appeal for greater unity between Catholics and Orthodox. At the time, Francis "shamefully" acknowledged the "mistakes" that the Catholic Church had inflicted on others over the centuries, actions which he said "were marked by a thirst for advantage and power."

A similar ecumenical gift was made by Pope Francis in 2019. According to the Catholic News Agency, the pope gave Orthodox Patriarch Bartholomew I of Constantinople a relic of St. Peter as "a confirmation of the journey that our Churches have made in drawing closer to one another.

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The three fragments, held by the Vatican since the 19th century, consist of a relief with the head of a boy, a bearded male head, and a part of a horse's head. The head of the boy was previously loaned to Greece in 2008.

The Parthenon was built in the 5th century BC as a temple to the goddess Athena and its marbles are viewed as the pinnacle of Greek sculpture.

Greece still has high hopes for the return of the Parthenon marbles which reside in London's British Museum. After reports of "secret" repatriation meetings between the Museum's chair George Osborne and Greek officials, the U.K. government confirmed it has no plans to change the law to facilitate their return.

The Associated Press contributed to this report.