Of course, any intervention to protect cultural sites must be carried out with great care. If the West were to intervene to protect world heritage sites but do nothing to stop the destruction of shrines and cemeteries that mean the most to local populations, it would do more harm than good. Aid to Syrians and Iraqis to protect buildings, monuments, libraries and museums may need to be distributed covertly.

But amid overwhelming evidence that the Islamic State’s barbaric campaign against culture amounts to a war crime, the world must be ready to use force to stop it. Abdulameer Al-Dafar Hamdani, an Iraqi archaeologist now studying at Stony Brook University, notes that the ancient Assyrian cities under threat in northern Iraq, including Hatra, Nimrud, Nineveh and Khorsabad, are in remote areas far from civilian villages. Air power could readily detect insurgents moving toward them, he argues, and a single coalition strike, well away from the sites themselves, would make clear that the West is prepared to protect them.

“It’s a military issue,” he told me. “For now, it is the only way.”