The fires of fanaticism
Among ignorant Westerners, the very name "Timbuktu" has long been shorthand for the boondocks or for a place incredibly remote, but in fact the city has for centuries been a major trade and cultural center for west Africa and the Sahara. As such, it is host to two archives containing thousands of irreplaceable medieval books and manuscripts embodying the culture and history of the region -- an aging library and a newly-built research center using modern techniques to preserve and study the centuries-old texts.
Before leaving Timbuktu, the Islamists burned down both buildings.
Why would they do this? It's of a piece with the Taliban's infamous destruction of the Bamiyan Buddha statues, or the rioting and threats of violence over the Danish Muhammad cartoons or Rushdie's The Satanic Verses, or the destruction and banning of books in Europe centuries ago when Christianity had the upper hand there. Religious fanatics cannot countenance the very existence of ideas that clash with their own. Libraries and historical archives worthy of the name are completist, not orthodox; they preserve texts of all kinds, not just those reflecting the "correct" viewpoint. And so, to the fanatic, they are citadels of deviant thought, best annihilated.
In Timbuktu the Islamists also destroyed the tombs of several Sufi saints, even though these were Islamic monuments. Why? Because the veneration of saints is a feature of Islam syncretized with local non-Islamic practices, in west Africa and elsewhere, and thus anathema to strict orthodox Islam. True fanatics seem to hate most of all those who practice a slightly "wrong" form of the "right" religion. Consider the violence and destruction wrought by Sunnis against Shiites and vice versa in Iraq, and by various Muslim factions against others in Pakistan, or the hideously bloody wars between Catholics and Protestants in Europe centuries ago when people there still took religion seriously. Heretical belief is as bad as unbelief, if not worse.
This mentality is far from unknown in our own country. There have been symbolic burnings of Harry Potter books, and the Christian Right's constant denunciations of science, especially the theory of evolution, stem from the same mind-set.
Religion inevitably tends in this direction because its beliefs are inherently ridiculous and cannot compete or, in the long run, even survive in an open competition of ideas. Even the presence of rival religions is dangerous. Where a diversity of thought is allowed to exist, religion withers away, as has been happening for decades in all advanced countries. Eruptions of fanaticism such as modern jihadism or our Christian Right are the panic-stricken hysterics of the shrinking core of fanatics who know their narrow orthodoxy is losing out.
Oh, and it turns out that quite a few of Timbuktu's medieval texts were saved after all; preservationists and local people had removed them from the archives before they were burned, because they knew what the Islamists are like and knew that they would be likely to destroy the manuscripts. It's also reported that local people celebrated when the French drove the Islamists out, even though they are themselves mostly Muslim. Normal people all over the world, it seems, recoil from religious fanaticism when they get a real taste of it.