For a half-century, Khaled Asaad devoted his life to the antiquities of Palmyra, a UNESCO Heritage site located northeast of the Syrian capital, Damascus. A scholar of Aramaic, Asaad wrote extensively about pre-Islamic life in Syria and was a fixture of international archaeological conferences. But the ruins he worked among could not preserve his life. On Tuesday, militants from the Islamic State beheaded Asaad in a Palmyra town square after he refused to divulge the location of artifacts coveted by the group. ISIS then hung the 82-year-old’s corpse from a Roman column.

Gruesome executions are an integral aspect of the Islamic State’s ruling style, but this killing illustrates the crucial role antiquities play in ISIS’s day-to-day governance. Part of this is symbolic: Muslim fundamentalist groups have long had a contentious relationship with cultural artifacts, particularly those that predate the rise of Islam in the 7th century A.D.

After it captured Palmyra in May, ISIS sought to quell fears it would destroy the ancient city, saying it would spare the ruins and monuments. But, a commander for the group said, “we will … pulverize statues that the miscreants used to pray [to].” The group was true to its words, sparking international outrage by releasing videos displaying destruction of ancient Islamic shrines.

But the ruins of Palmyra are a valuable economic commodity. Syria’s archaeological treasures fetch high prices in the international black market and are a crucial revenue stream for ISIS. In this, the group is continuing a process that began long before its inception: Illicit trade in antiquities existed in Syria even before the 2011 civil war uprooted centralized control. In July, BuzzFeed profiled a Syrian trader who smuggled ancient goods across the country’s porous border to Turkey, where items such as statues can sell for hundreds of thousands of dollars.

According to the Financial Times, ISIS’s trade in archaeological goods has risen because other revenue streams—such as oil—have become less practical. In that context, the group’s announcement it would preserve Palmyra makes more sense.