In History, the details are always hard to catch, yet always worth knowing. This long post at History for Atheists, worth absorbing in full, makes a number of discordant points about the Myth that the Great Library of Alexandria was destroyed by a Christian mob in 390 AD, thus setting science and technology back a thousand years. I will state them below in brief, and you may read the post in full.

1. The Great Library of Alexandria was not the only Great Library of the Ancient World. It did not “contain all the wisdom of the ancient world”.
2. The Great Library of Alexandria was a research institution, a Mouseion, devoted to the Nine Muses, which is to say, they were a product of Pagan religious inspiration, the worship of the gods.
3. Consequently, most of the scholarship done at the Mouseion was focused on textual criticism and poetry, and not very much on what we moderns would call science.
4. The Ancient Greeks and Romans didn’t really do science as we understand it today. Which is to say, their natural philosophy was largely inductive, not empirical, and they did not apply this philosophy to improving the technology of their culture.
5. The Mouseion had almost certainly ceased to exist by 390 AD. A series of sackings of the city by Romans, beginning with Julius Caesar, greatly diminished the value of the place.
6. What was destroyed in 390 AD was a daughter library, the Serapaeum. As with the Mouseion, the Serapaeum was first and foremost a pagan temple, devoted to the worship of the hybrid Greek-Egyptian God Serapis. It’s destruction in 390 was the result of a long series of hostilites between the pagan and Christian populations of the city. Which is to say, it was the result of a war between rival religious traditions, and not a war between religion and science. And according to primary sources, there may not even have been a library in the Serapaeum at the time.

Again, Read the Whole Thing (Hat Tip: Vox Populi)