The marbles from the Acropolis in Athens are properly in the British Museum in London because Lord Elgin paid the government for them when he was the British ambassador there and there was not any law that prohibited the shipment of such antiquities out of the country at the time.
The British government has further rationalized the current situation by arguing that, by shipping them to London, they have been preserved for posterity, whereas, had they remained in Athens, they would have suffered the same fate as the Parthenon, partially destroyed when the explosives stored there exploded, and besides, the Greek government does not have a proper place to exhibit them for the world to see.
The last rationalization is now simply not true; the recently completed Acropolis Museum displays very professionally five of the original six Caryatids from the porch of the Erechtheion. (Elgin took only one, along with the marbles from the Parthenon's pediment.) They and their kidnapped sister have been replaced in the Erechtheion with copies, and the five original maidens now in the Acropolis Museum have had centuries of grime removed by a laser technology developed by the conservators at the Museum. (See The New York Times of July 8, 2014, pp. C1-2.) (Better treatment than their sister in London has received.)
But the main contention that all the marbles Elgin bought are properly in London is, to use a polite English expression, hogwash. It does not even deserve the honorific title of "myth."
When the Ottomans conquered and occupied Greece, that did not give them title to the Acropolis, with the right to sell whatever they wanted to sell. That, I believe, is the myth of the British Museum's claim that the marbles have been "properly bought and paid for."
A smarter-than-me Yale Law School classmate has pointed out to me that, under international law, the Ottomans were free to treat property in occupied Greece as theirs, so the "sale" transferred title properly. He cites Banco Nacional, 376 U.S. 398, where the U.S. Supreme Court refused to question Cuba's right to seize sugar in Cuba and sell it to a sugar broker. The decision was based on the Act of State Doctrine, which does not permit an American court to challenge an act of a foreign sovereign.
The only thing I know about public international law (the law between governments, as distinguished from private international law) is that there is not a specific statute of limitations, the time after an actionable event within which a claim must be asserted. In public international law, a court will hear a claim made many years after the event if the respondent has not been prejudiced by the passage of time. (It is called "the period of prescription." See my description of the difference in my lecture on international commercial arbitration linked to my bio on this site.) I do not know when Greece first asked for the return of the Acropolis marbles, surely it was as soon as the Ottomans had left, but I cannot think of how the UK has been prejudiced by the fact that many years had passed since Lord Elgin shipped the marbles to London.
More important, the U.S. Act of State Doctrine is not applicable in a foreign court established to adjudicate disputes between states. The whole premise or raison d'être for the existence of the International Court of Justice and the Permanent Court of Arbitration in The Hague is to adjudicate acts of governments.
And perhaps equally significant, the world has changed since Lord Elgin took the Marbles with him. In recent years both Christie's and Sotheby's have been praised for their diligence in provenance research before accepting art works for auction and for their diligence in arranging settlement agreements for art looted by the Nazi from Jewish collectors. The German Government runs a Lost Art Internet Database. In the United States there is a Presidential Commission on Holocaust Assets. Museums have returned foreign treasures voluntarily, e.g., Yale has recently returned what Hiram Bingham brought home from Maichu Pichu in Peru more than a century ago.
I respectfully suggest that the Permanent Court of Arbitration would conclude that a Greek claim for the return of the marbles is not time-barred. I also believe that that tribunal would reject the applicability of Banco Nacional and more likely than not would follow the numerous precedents of U.S. and European courts that have required the return to the former owners' surviving family members of the assets taken from Jews sent to Dachau and Auschwitz. The depredations of the Nazis may have been the straw that broke the proverbial camel's back in world opinion of where historic artifacts belong.
Σφιξτε τις ζωνες ασφαλειας παρακαλω! (Tr: Fasten your seatbelts, please)
by John W. Barnum