Ross Burns' website, Monuments of Syria, chronicles the historic sites damaged in the present conflict.

The brutal beheading of Khaled al Asad, former Director of Antiquities in Palmyra, and the detonation of the beautiful little Temple of Baalshamin, built just after the Roman emperor Hadrian visited the desert city in AD 130, appear to have caught the world's imagination in a way that has had few precedents for some time in the savage conflict in Syria.

In light of the prolonged barbarity conducted by all sides in the conflict it may seem strange that these two events have rocketed to the top of the agenda of a conflict well into its fifth year. As the shock waves of the war have spread — with tens of thousands of victims of the conflict flooding Macedonian railway stations; a generation of children spending their formative learning years in a world of normalised violence; fatalities of the conflict reaching well over 240,000; a good half of Syria's population displaced; a sizeable proportion of the country's housing stock in ruins — why does one death and one 2000 year-old temple give us pause?

The answer is because ISIS has successfully opened a new front which it hopes will hasten the fall of the Assad regime. The threat of destruction of Syria's great array of significant ruins — treasures not only appreciated by connoisseurs of Classical civilisation or scholars of arcane Neo-Hittite palaces but by ordinary Syrians — is now pressed into service to stoke the conflict.

In the years before ISIS spread across Syria from Iraq, many monuments disappeared, with little to mark their passing. The loss of the only Seljuk-era structure in Syria, dated in the decade before the Crusades, caused a mild ripple, but a number of other notable buildings in frontline Aleppo disappeared into the caverns of the Islamist tunnel bombs with barely a mention. The funeral mosque of the most successful of the sons of that great Islamic hero Saladin lies in a pile of rubble at the foot of the Aleppo Citadel. Two of the major early works of the Suleiman the Magnificent's architect, Sinan, are either pulverised or reduced in part to tumbled stones.

ISIS's arrival in Syria's historic heartland, notably their seizure of Palmyra, brings a new dimension to this apparently mindless destruction. The fact is, of course, that it is not mindless at all; it has a very specific purpose.

In the distant past, iconoclasm was a selective tool of both Byzantine and Islamic regimes intent on effacing the memory of earlier cultures. Much of the destruction in Syria for the first three years of the conflict, however, was a by-product of the fighting and the loss of any framework of government to keep petty or major crime at bay. With the rise of ISIS to supremacy in many parts of the country, stage-managed destruction is itself the message.

Having moved on from blowing up remote rural shrines, treasured for decades by local villagers, ISIS has advanced to bigger-picture stuff. And there is no bigger picture than Palmyra. This jewel of the desert was an elusive destination for seventeenth century European adventurers and for scholars tracing the cross-currents shifting across the poorly defined frontiers between Classical and Persian (even Chinese) worlds. Its temples, columned streets and tower tombs, stamped with a mixture of Greco-Roman, Mesopotamian and Semitic traditions, were largely left to slumber quietly over centuries.

ISIS sees them differently. The ruins are hostages in a war where savagery on all sides has redefined the unthinkable. We have seen how ISIS videographers contrive events such as the explosion of the Baalshamin Temple. They will continue their efforts to choreograph shock, to keep the world off guard and to use the ruins as weapons.

We don't know precisely why Khaled al Asad died but he represented a concept of Syria that ISIS cannot allow to survive. He was an archaeologist far removed from the Indiana Jones mock-heroic tradition. He was a doer and a scholar of integrity. He didn't excavate a patch of ground and then retire to his study. He was out and about every day, running his museum with its incomparable range of crisp limestone tributes to the dead, directing the conservation of new tomb finds. He was the picture of the archaeologist writ large, determined to show that there was much more to Palmyra than pretty columns or towering tombs. Under his direction, the city's Byzantine churches, early Islamic suqs and houses and even its first mosque were exposed. He showed Palmyra in all its complexity, its mixture of civilisations and faiths; and for that he had to die.