Story highlights Museums director Qais Hussain Rashid says ISIS militants are destroying antiquities

He says they sell parts of ancient carvings to criminals and antique dealers

ISIS controls Mosul and the ancient city of Hatra, known for its palaces, temples and statues

"I'm afraid they'll do something crazy there," Rashid says of ISIS fighters in Hatra

There's been no shortage of news coverage of the atrocities carried out by ISIS against the people of Iraq and Syria, from beheadings to massacres to selling kidnapped women into sexual slavery

What's less well known is the devastation the Sunni extremist group is wreaking on Iraq's priceless cultural heritage.

Thousands of years before the birth of Christ, the people of Mesopotamia mastered the first writing system, mathematics, astronomy, literature and law.

Iraq's past, however, is threatened by the nightmare of its present.

ISIS is not only at war with the Iraqi state, it's also at war with Iraq's very identity -- blowing up religious shrines, slaughtering and enslaving minorities such as the Yazidis, Christians and Turkmen, and executing its enemies.

And what it hasn't destroyed, ISIS is selling on the black market.

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Qais Hussain Rashid, director general of Iraqi museums, told CNN of the depredations carried out by ISIS militants.

"They cut these reliefs and sell them to criminals and antique dealers," he said, gesturing toward an ornate carving dating back thousands of years.

"Usually they cut off the head, leaving the legs, because the head is the valuable part."

Ancient city of Hatra at risk

The area around Iraq's northern city of Mosul, overrun by ISIS in June as Iraqi army soldiers fled, is replete with ancient ruins -- now in peril.

Rashid has particular fears about the preservation of the ancient ruined city of Hatra , or al-Hadr in Arabic, which dates back to the third century B.C. and is south of Mosul.

ISIS took over the site a few months ago, using it to store weapons and ammunition, to train fighters and to execute prisoners.

Established by the successors of Alexander the Great, Hatra became the capital of what some believe to be an early Arab kingdom that also included the fabled city of Petra in Jordan, according to the museum. It withstood attacks by the Roman Empire before falling in the third century A.D. to the Persian Sassanid Empire.

Standing within inner and outer walls studded by scores of towers are large numbers of architectural treasures reflecting its long and diverse history.

"There are palaces, temples and statues there, and ISIS is living among them," Rashid said. "I'm afraid they'll do something crazy there."

ISIS has also taken over Mosul Museum, turning it into an office to collect jizya -- a tax levied by the militant group on non-Muslims.

The fate of the antiquities there is unknown.

'People from another planet'

The U.N. cultural agency UNESCO has sounded the alarm over Hatra and other sites in Iraq, saying their preservation will play a role in any future peace.

"Protecting the lives of people, their cultural heritage and identity go hand in hand," the agency's director general, Irina Bokova, said at an emergency meeting in July.

She pledged that UNESCO would mobilize the United Nations "and the whole international community to safeguard Iraq's cultural heritage with particular emphasis on the fight against illicit trafficking in cultural property."

But while the conflict still rages, little can be done to protect artifacts on the ground.

This isn't the first time that Iraq's precious cultural wealth has been under threat. The country's history is full of catastrophes.

One of the worst was the Mongol sacking of Baghdad in 1258, when it's said the Tigris River ran red and black, with blood and the ink of thousands of priceless manuscripts.

But to Rashid, the Mongols' barbarity pales in comparison with that of ISIS.

"They are people from another planet," he says. "They take pride in nothing. Their mentality is completely petrified. They don't think of all this as the accomplishments of humanity."