Here’s a really good essay at Science Musings about the Crusades, jihad, and how science came to the western world.
Question: Who said, “Whenever [one] hears [our] religion abused, he should not attempt to defend its tenets, except with his sword, and that he should thrust into the scoundrel’s belly, as far as it will enter”?
Semimonastic orders of Christian knights were established with the express purpose of slaughtering Muslims, in presumed obedience to Christ’s injunction in Matthew’s Gospel: “If anyone wants to be a follower of mine, let him renounce himself and take up his cross and follow me. For anyone who wants to save his life will lose it; but anyone who loses his life for my sake will find it.”
The rules of these medieval Christian military orders — the Templars, the Hospitallers — read like the rules of a Taliban training camp, right down to the prohibition against shaving beards. To adorn one’s clothes or even to wear shoelaces was deemed to partake of the decadent lifestyle of the enemy. The whole bloody enterprise was sustained by an unalterable conviction that God was on the Christian’s side.
As Christians fought Moslems in the Holy Lands and Spain, they came into contact with a kind of intellectual inquiry, now called science, that had been invented in the Eastern Mediterranean before either Christianity or Islam appeared on the scene. This new way of thinking made no reference to gods or miracles. It was founded on close observation of nature and mathematics.
Science and mathematics were cultivated in the great Islamic centers of learning — Baghdad, Cairo and Grenada — at a time when Europeans were mostly interested in bashing each other over the heads and rooting out heresy. Crusading knights were commonly illiterate. But literate camp followers brought scientific learning home from the East and sparked Europe’s Scientific Revolution and Enlightenment.
Why science and mathematics found their most fertile soil in the West, rather than, say, in China or Islam, is a question historians love to debate. The rise of the secular state in Europe and America certainly helped.