There is an ancient (apocryphal)  story about the destruction of an ancient historical site, the Great Library of Alexandria.  While ancient accounts of its partial destruction varies, it was an apocryphal order from Caliph Omar to victorious Arab armies, which had by then overrun Egypt, which led the ancient library to its destruction.

Quite simply:

If the books agree with the Quran, we do not need it.   If the books oppose it, destroy them.

Now a new Caliph stretches his empire across much of Syria and Iraq.  And his orders are the same: if the historical ruins and cities “oppose Islam” (even if it pre-dates it) then destroy them.

What do you think will happen to Palmyra, the ancient crossroads of the Roman, Persian and Greek civilizations?

UPDATE (04-04-2016):  A month or so ago, the Syrian government retook Palmyra from ISIS.  At least partially, Palmyra was preserved, but the losses inflicted to it–like the Temple of Bel–are irreplaceable.  At least we can be thankful that the worst did not happen.