LONDON -- The UNESCO World Heritage site of Palmyra, Syria, was only the latest casualty in the destruction of the world's shared cultural legacy.

ISIS has demolished precious artifacts and archaeological sites from Syria to Iraq. But CBS News correspondent Clarissa Ward says, out of sight and off camera, what isn't destroyed is being quietly sold on a black market that reaches Europe and even the U.S.

To get a firsthand look at this underground world, Ward's producer Jennifer Janisch posed as a buyer and made contact with Omar, a Syrian living in Turkey who offers looted artifacts to international buyers. He sent us images of coins and statuettes, jewelry and ancient books -- likely a mixture of real and fake items, experts told CBS News.

Omar claimed to have mosaics freshly ripped out of the ground in Syria. Janisch and Ward met him in Istanbul and recorded the meeting on hidden cameras. Archaeologist Amr al-Azm joined the CBS News undercover team to help authenticate the mosaic.

Omar

Two nervous young Syrians took us to a run-down apartment on the outskirts of town, and there it was; a beautiful roman mosaic, nearly 2,000 years old and, as we learned later, potentially worth $100,000.

They said it was taken out of Syria only recently -- one of seven mosaics they had dug up in the ancient city of Apamea, one of Syria's most significant archaeological sites. Satellite photos show the ground around Apamea pockmarked with the telltale holes left by looters.

Ward and Janisch then moved to their waiting van, where they were also offered Roman glass stolen from a tomb.

An antiquity allegedly looted in Syria and offered to CBS News by a Syrian smuggler named "Omar," based in Turkey. These artifacts have not been evaluated as to their authenticity. Omar

There the negotiating began: $200,000 for the mosaic, they said, but that quickly dropped to $60,000. They were eager to get the illegal piece off their hands.

"Clearly this is part of the tragedy of the war in Syria," said al-Azm, the archaeologist. "The fact that they feel that this is the only way they can essentially survive and feed their families... Syria has such a rich history, rich cultural heritage."

A history al-Azm said is being "totally pillaged and destroyed... Syria's cultural heritage has become a casualty of war."

In Gaziantep, Turkey, near the Syrian border, we met Abu Walid, who told us he felt he had no choice but to loot and sell artifacts.

"There is no more work in Syria," he said, explaining that people have to sell artifacts or join an armed group, obliged to either fight or steal. ISIS is the primary beneficiary, making tens of millions of dollars through the illegal trade. The group issues licenses to looters to dig in their territory.

"If you find an artifact, you take 80 percent and ISIS takes 20 percent," he said. Or, if the equipment used to unearth the treasure belongs to ISIS, they take a 40-50 percent cut instead.

"The illegal traffic in looted antiquities is buying the bombs and the bullets that are killing so many," U.S. Marine Col. Matthew Bogdanos, who led the investigation into the 2003 looting of the National Museum of Iraq, told CBS News. Now he prosecutes antiquities cases as an assistant district attorney in the U.S.

"In a surprisingly small number of steps, you can go from the looter in ISIS-controlled territory to the smuggler who gets it out of the country... to a gallery owner who provides forged documentation... and ultimately getting a buyer making its way to the four destination points of New York, London, Paris and Tokyo," Bogdanos said.

He said he and his colleagues have seen evidence of artifacts "looted by ISIS or under the authority of ISIS" ending up on the markets in London and even New York.

CBS News has learned there are multiple ongoing investigations into ISIS-looted artifacts that have reached the U.S., but the cases are very difficult to prove because it's so easy to forge documentation about the provenance and the authenticity of these objects.