According to San Jose State University, the destruction of this priceless treasure was a stroke of the most unimaginable bad luck. If Byzantine Egypt had been taken by one of the later Islamic conquerors, this irreplaceable collection would have been counted amongst the finest of the spoils of war to fall into a victor's hands.
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.
This is what Carl Sagan imagined the library looked like.
I love the idea that words, histories, stories, thoughts and ideas have always been important enough to write them, keep them, and make them available to the masses for reference and reflection. Legend has it that there was an inscription above the shelves that read: "The place of the cure of the soul."
More about the Library of Alexandria at The History Channel.