Greece is stepping up the pressure on Britain to return one of the ancient world's most valued treasures: the Elgin Marbles, sculptures removed from the Parthenon in the early 1800s and housed in the British Museum.

Greece announced earlier this month that, after years of delays, it would open its new Acropolis Museum in Athens in September. The modern structure would allow it to properly display and preserve the sculptures from the fifth century B.C.

And that, Greek Culture Minister Michalis Liapis said, "will be a strong argument against those who oppose the Marbles' return."

Not so, British Museum spokeswoman Hannah Boulton says. The Marbles, she says, won't be going to Greece — not out of fear they cannot be preserved, but because they fit in the museum's goal of displaying mankind's shared cultural heritage. "They should remain part of the collection," she says.

The dispute over the Elgin Marbles is part of a worldwide struggle over who owns antiquities. More nations are demanding a return of what they call their cultural heritage that they say was looted over the years, most often by richer nations. Museums, including major ones in the USA, are often the targets.

Greece, Italy, China and a host of other countries, such as Cambodia, are demanding that ancient treasures be given back. They base their claims on new "cultural property" laws that lay claim to art and artifacts inside their borders and a 1970 United Nations convention banning the export of works without a license.

More museums turning over property

A number of museums are complying, and governments are increasingly cooperating.

In recent years, the Boston Museum of Fine Arts, the Metropolitan Museum of Art in New York and the J. Paul Getty Museum in Los Angeles have returned works to Greece or Italy.

Last week, Britain's Scotland Yard seized two paintings worth about $20 million at Italy's request. In January, U.S. federal agents raided four Southern California museums in search of art possibly looted from Southeast Asia or from Native American sites.

"A new wind is blowing," Liapis told an international conference on the return of antiquities earlier this month in Athens. The conference was organized by UNESCO, the United Nations Educational, Scientific and Cultural Organization. "More and more museums are adopting tighter ethics codes, and governments are promoting bilateral and international cooperation."

The trend of returning works to their presumed land of origin isn't without its critics, however. They question whether today's governments are legitimate heirs of ancient civilizations or whether such antiquities, such as the Elgin Marbles, belong to all mankind.

"No one owns antiquities," says James Cuno, director of the Art Institute of Chicago, who argues that nations are invoking cultural property laws more for political reasons than to preserve or share ancient works with the rest of the world. "It's better to believe that they belong to all of us."

Cuno, who lays out his arguments in his forthcoming book Who Owns Antiquity, says the British Museum has a rightful claim to the Elgin Marbles and that offering them to the public as part of an encyclopedic view of man's cultural development is legitimate.

Dispute has raged for centuries

The dispute over the Elgin Marbles is a longstanding one.

Lord Elgin, a British diplomat, removed about half of the sculptures and friezes remaining on the Parthenon between 1801 and 1805. He had the permission of the Ottoman Empire that then ruled Greece. The British Museum obtained them from Elgin in 1816 and has displayed them free to the public since. Last year, 5.4 million people visited the museum.

Greek governments since World War II have questioned the ownership of the Marbles and demanded their return. The museum has steadfastly refused. "Our position hasn't changed," Boulton says. Displaying the Marbles with the Rosetta stone, plus Egyptian, Roman and other works from around the world, helps "tell a much broader story" of man's cultural development than if they were shown at the Acropolis with other Greek artifacts, she says.

Amid the struggle is a growing effort to find some middle ground in which works can be preserved and the whole world has a chance to see artifacts from different parts of the world in nearby museums.

Cuno suggests that archaeologists, museums and nations return to a pre-World War II policy called "partage," in which everyone could share. Under it, wealthier universities or foundations would underwrite the archaeological work in poorer countries and then share the finds with the host nations.

He says partage led to great exploration, knowledge and to great museum collections around the globe, including in such nations as Egypt and Iraq that didn't have them before. The result, he says, is more people around the world could see works in more museums.