The Islamic world acted as the west's library during the dark ages yet did alomst nothing with that knowledge themselves.
Early in the year A. D. 642, Alexandria surrendered to Amrou, the Islamic general leading the armies of Omar, Caliph of Baghdad. Long one of the most important cities of the ancient world and capital of Byzantine Egypt, Alexandria surrendered only after a long siege and attempts to rescue the city by the Byzantines. On the orders of Omar, Caliph of Baghdad, the entire collection of books (except for the works of Aristotle) stored at the Library of Alexandria were removed and used as fuel to heat water for the city's public baths.
From http://www.mediahistory.umn.edu/indextext/Alexandria.html