ISIS is fueling its terrorism by plundering ancient relics and selling them for millions of dollars. The buyers are mostly Westerners who are funding ISIS's terrorism in exchange for priceless artifacts.

ISIS is famous for destroying ancient artifacts. ISIS militants have wielded sledgehammers, drills, explosives, and tractors to smash artifacts thousands of years old. In one video, a religious spokesman declared:

“These idols and pagans for people in the past centuries were worshipped instead of Allah. When Allah ordered to destroy and remove them, it was an easy matter. We don't care, even if it costs billions of dollars.”

The relics, however, are not worthless to ISIS. Far from it. ISIS makes millions of dollars each year by selling artifacts instead of destroying them. Plundered relics are ISIS's second-largest source of funding, just after oil, as reported by the Wall Street Journal.

The exact revenue generated by ISIS's plundering is uncertain due to the murky nature of the black market. Estimates range from hundreds of thousands of dollars to over $100 million.

The looting itself is nothing new. Opportunists have raided archaeological sites for millennia. But ISIS has transformed this looting into an organized gold mine.

The caliphate controls thousands of archeological sites, as well as numerous museums. ISIS's antiquities division exploits Iraq's and Syria's rich archeological history as if the nations' cultural heritages were a natural resource. The antiquities division issues excavation licenses and levies a 20 percent tax on looting.

As a source of revenue, the antiquities trade contains significant advantages for the terrorist state. Unlike taxes, kidnapping, and extortion, plundered relics do not risk alienating the locals. Nor are excavation sites typically airstrike targets, according to a report by the Foundation for Defense of Democracies.

The United Nations and Western governments have tried to crack down on ISIS's smuggling. In 2015, the U.S. State Department posted a $5 million reward for anyone with information that could “significantly disrupt” ISIS's antiquities or oil trade. The U.N. Security Council also banned all trade in looted antiquities coming out of Syria and Iraq.

Such measures, however, have met little success.

Attempts to choke ISIS's antiquities trade face a series of obstacles such as inconsistent laws, private citizens looking to profit, and the ease of smuggling smaller items like coins. Authorities must also combat the experience of smuggling networks, many of which were operating for years before ISIS formed and overcome ISIS's use of social media to bypass the middleman and reach buyers directly.

Valuable relics from the battlefield flow through trade routes, often following the same paths as refugees, reported the New Yorker. Eventually, most of them find their way into the hands of wealthy Westerners — Europeans, Americans, and especially New Yorkers, according to the WSJ.

One piece, dated to 8500 B.C., sold for $1.1 million, reported BBC.

“The main buyers are, ironically, history enthusiasts and art aficionados in the United States and Europe — representatives of the Western societies which IS has pledged to destroy,” Yaya J. Fanusie said in a report by the Foundation for Defense of Democracies.

“This means that those countries purportedly leading the fight against IS are simultaneously funding the enemy through the antiquities trade.”