NEW YORK, NY.- For decades, there was a swashbuckling aspect to collecting by American museums. In the 1960s, for example, some museum curators embraced the chase for prized artifacts as if it were big game hunting.

Thomas Hoving, a Metropolitan Museum of Art curator who later became its director, took particular pride in his ability to outsmart rivals in the global pursuit of masterpieces. In one instance he recalled spiriting a Romanesque relief from a Florentine church out of Italy with the help of a dealer who, Hoving said, often stashed objects under a mattress in his station wagon.

“My collecting style was pure piracy,” he boasted, “and I got a reputation as a shark.”

Today many U.S. museums are facing a reckoning for their aggressive tactics of the past. Attitudes have shifted, the Indiana Jones era is over, and there is tremendous pressure on museums to return any looted works acquired during the days when collecting could be careless and trophies at times trumped scruples.

Although the tide turned more than a decade ago, the pace of repatriations has only accelerated in recent years. In just the past few months, museums across the United States have returned dozens of antiquities to the countries from which they were taken.

The J. Paul Getty Museum in Los Angeles returned three precious terra cotta figures to Italy. The Denver Art Museum shipped four antiquities back to Cambodia. The Smithsonian Institution returned 29 Benin bronzes to Nigeria. And the Manhattan district attorney’s office seized 27 looted artifacts from the Met, which are headed back to Italy and Egypt.

For some, the number of restitutions has become unsettling. Museums, like public libraries, have long enjoyed an exalted status as places that promote erudition by permanently preserving and displaying the significant objects that define human history and culture.

Consider, for example, the mounting pressure on the British Museum to return the Elgin marbles that once graced the Parthenon. They were acquired at the dawn of the 19th century when the Ottoman Empire ruled Greece. The British view the sculptures and bas-reliefs as legitimately transferred by the Ottoman authorities. The Greeks argue that the Turks, as occupiers, lacked the moral authority to dispense with their history.

In America, critics of the surge in returns worry that museum collections built over time by scholars and imbued by a sense of context are being randomly depleted. Should U.S. audiences, they ask, be deprived access to iconic objects that they suggest belong, not to individual nations, but to humankind?

Leila Amineddoleh, an art and cultural heritage lawyer, has suggested that such thinking is outdated.

“Arguments against repatriation are sometimes supported by paternalistic and patronizing arguments,” she wrote, “asserting that western collectors and archaeologists ‘discovered’ these objects and have superior knowledge of them.”

Experts say a significant change in attitudes about collecting dates to 1970 when nations began ratifying a UNESCO treaty to stem the trade in illicit artifacts. Awareness of the problem expanded further 20 years ago when antiquities looting during the Iraq War made clear the scope of that black market.

But most significantly, U.S. authorities, both local and federal, have made the return of looted cultural heritage more of a diplomatic and law enforcement priority. U.S. Homeland Security Investigations reports returning more than 20,000 items since 2007, largely seized from dealers and collectors, but also found in many of America’s most prestigious museums.

“There has been a broad agreement for decades that objects that were stolen in violation of law should be returned, but what has changed is the amount of time and focus spent on this kind of crime and the political will to pursue it,” said Donna Yates, associate professor, criminal law and criminology at Maastricht University in the Netherlands.

Museums do show a heightened sensitivity to the integrity of their collections and have returned illicit objects based on their own research. But experts say most museum repatriations of recent years have been sparked by government claims or U.S. law enforcement efforts.

“There is a sense that the U.S. should not be the repository of the world’s stolen property,” said Stefan Cassella, a former federal prosecutor.

Experts say the 1970 UNESCO convention helped redefine acceptable behavior when it came to antiquities. Nations pledged to cooperate and follow best practices to curb the import of stolen items.

Although the treaty governed the conduct of nations, not institutions, museums began to set guidelines that aligned in spirit with its principles. Many agreed, for example, not to acquire an artifact without clear, documented evidence that it had left its country of origin before 1970, or had been legally exported after 1970.

Still, the ethos of collecting hardly changed overnight.

“When I first entered the world of curators, it was the Wild West, ‘1970’ notwithstanding,” said Gary Vikan, who was a curator in the 1980s and later became director of the Walters Art Museum in Baltimore. “Curators and museum directors wanted to get important works. You wanted to be the one that gets that icon, that sculpture, that bronze.”

Some art world experts are not convinced that U.S. museums have fully embraced a new ethos of transparency and internal scrutiny.

They point to what they consider to be loopholes in the Association of Art Museum Directors guidelines on the acquisition of artifacts. The association, which serves as the industry’s ethical compass, discourages the acquisition of any object without a documented provenance before 1970, unless it has an official export permit. But the guidelines allow museums to accept such an artifact if they list it on an online registry where they report whatever provenance information they do have and a justification for taking it in.

To date, museums have posted 1,754 objects on the exception registry.

The association has spoken of how seriously it and its member organizations view the issues of looting and cultural heritage. But Patty Gerstenblith, the director of the Center for Art, Museum and Cultural Heritage Law at DePaul University, called the registry’s standard “very, very loose.”

“It looks like a fig leaf,” she said.

Vikan, the former museum director, said that while he fully endorses repatriation efforts, the cost for museums goes beyond the loss of artifacts already in a collection. Given their limited acquisition budgets, American museums have relied on donated antiquities and now donors who lack full paperwork can be reluctant to make gifts, and museums are reluctant to accept them.

But he does not worry that large museums, which typically display only a fraction of their holdings, will be significantly hurt by more robust repatriation efforts.

“If anyone tells me that sending the Elgin marbles back to Greece, that somehow the British Museum will be empty, it’s nonsense,” he said.

This article originally appeared in The New York Times.