With a half-dozen wooden art shipping crates laden with a smorgasbord of ancient artifacts as a backdrop, Italian and American officials on Wednesday celebrated the continuation of a 25-year collaboration that has returned thousands of illegally trafficked objects to Italy.

“The United States is, in every respect, Italy’s closest ally in the fight against the illicit trafficking of cultural property,” Italy’s culture minister, Alessandro Giuli, said at an event staged to recognize the return to Italy of trafficked objects and stolen artworks recovered from American museums, auction houses and private galleries over the past year.

The artifacts, which included Etruscan vases, Roman-era bronze and marble statues and busts, but also Byzantine coins and a 13th-century manuscript page, were identified after investigations by Italy’s art theft police in collaboration with different U.S. agencies, among them the Manhattan district attorney’s office, the F.B.I. and Homeland Security Investigations.

“Our two governments are well aware that theft, illegal excavations, and illicit exportation are crimes committed against the public good,” and both countries are “committed to combating this threat to the world’s cultural heritage in increasingly innovative, and effective ways,” Mr. Giuli added.

The photo-op camaraderie came at an especially low moment in U.S.-Italy relations. Earlier this month, after President Trump criticized Pope Leo XIV, Prime Minister Giorgia Meloni got a Trumpian tongue-lashing for having jumped to the pope’s defense.

Ms. Meloni said last week that she hadn’t spoken to Mr. Trump since their spat, but she expressed her support to the president after a gunman attempted to attack him over the weekend.

The at-times rocky relationship between art-rich Italy and art-hungry American museums and collectors was encumbered for decades by judicial investigations and court cases that often ended with a begrudging restitution of artifacts. Many cases remain open, like Italy’s claims on a bronze statue at the J. Paul Getty Museum in California.

In 2000, the two countries reached a cultural property agreement regarding importation restrictions that “has become a cornerstone of international efforts to combat the illicit trafficking of cultural property,” Italian officials said earlier this year at a commemorative event for the agreement.

Patty Gerstenblith, the director of the Center for Art, Museum and Cultural Heritage Law at DePaul University, said in an interview that the agreement has “been very effective in efforts by U.S. law enforcement in preventing undocumented antiquities from entering the U.S., returning these, and as a training tool for law enforcement.”

She added that it has also been useful in establishing a framework of cooperation between the two countries in cultural heritage, and encouraging loans to U.S. museums.

The agreement, renewed last December, covers import restrictions and only federal agencies can enforce it. In recent years, the Manhattan district attorney’s office in New York, though not a participant in the agreement, has taken center stage in multiple high-profile restitutions to Italy.

According to its own records, since its creation in 2017, its Antiquities Trafficking Unit has recovered more than 6,200 antiquities valued at more than $485 million, and has returned more than 5,860 to 36 countries.

The trove of nearly 340 artifacts returned on Wednesday showed the scope of the collaboration with American agencies.

Each object is the protagonist of its own nefarious back story.

The most prized piece, investigators said, was a marble head of Alexander the Great that was stolen from a Rome museum in 1960. It “was acquired in good faith” by Alan Safani of the Safani Gallery in 2017, according to a statement by the Manhattan district attorney’s office, but was seized by that office a year later. The gallery opposed the restitution and instituted a judicial process before a federal court of New York, which ruled in Italy’s favor last year.

“Protecting cultural heritage strengthens the rule of law and builds trust between governments and people,” Tilman J. Fertitta, the American ambassador to Rome, said at the ceremony. “When stolen art returns, both nations benefit. Italy regains its history, and the United States reaffirms its commitment to justice and cultural preservation.”

Also back is a first-century bronze winged satyr identified a year ago in an auction catalog, 50 years after the work had been stolen from archaeological deposits at the Herculaneum excavations.

For their part, Homeland Security Investigations assisted Italy in recovering 15 gold coins dating to the Byzantine era, part of a theft in 2009 in which 388 gold coins were stolen from the Archaeological Museum of Parma. They were tracked down in various specialized auctions.

The F.B.I. recovered from Los Angeles dozens of ancient artifacts in bronze, clay and marble that one investigator identified as having belonged to Jerome Eisenberg, an antiquities dealer who died in 2022. Investigations ascertained “their origin from clandestine excavations of Magna Graecia necropolises carried out in central-southern Italy, with the consequent illicit export to the United States,” the Italian authorities said in a statement.

More than 20 of the pieces focused on at the ceremony had been seized from the Metropolitan Museum in New York by the Manhattan district attorney’s office. Nine of the artifacts from the Met were part of a restitution announced in March that also included six rare books stolen from a Jesuit archive in Rome that had been appraised at $400,000.

The Met objects included two Greek ceramic drinking cups from about 500 B.C., a pair of Roman silver drinking cups from around the first century and a pair of gold earrings from the fifth century B.C.

In a statement this year, the Met said it had an “ongoing commitment to responsible collections stewardship.”