Did Christians burn the Great Library of Alexandria?

Question

The Great Library of Alexandria was one of the wonders of ancient civilisation having collected many thousands of scrolls containing knowledge and literature from across the known world.

The 2009 movie Agora is partially about its destruction and tells this story (my emphasis):

When the Christians start defiling the statues of the pagan gods, the pagans, including Orestes and Hypatia's father, ambush the Christians to squash their rising influence. However, in the ensuing battle, the pagans unexpectedly find themselves outnumbered by a large Christian mob. Hypatia's father is gravely injured and Hypatia and the pagans take refuge in the Library of the Serapeum. The Christian siege of the library ends when an envoy of the Roman Emperor declares that the pagans are pardoned, however the Christians shall be allowed to enter the library and do with it what they please. Hypatia and the pagans flee, trying to save the most important scrolls, before the Christians overtake the library and destroy its contents

Carl Sagan told a similar story in his series Cosmos (see this clip from about 3:30 in).

This version of the story has been frequently repeated as an argument about the irrationality of religion, but it has been disputed. For example, David Bently Hart (commenting on the movie) says the following:

The story he repeats is one that has been bruited about for a few centuries now, often by seemingly respectable historians. Its premise is that the Christians of late antiquity were a brutish horde of superstitious louts, who despised science and philosophy, and frequently acted to suppress both, and who also had a particularly low opinion of women.

Thus, supposedly, one tragic day in a.d. 391, the Christians of Alexandria destroyed the city’s Great Library, burning its scrolls, annihilating the accumulated learning of centuries, and effectively inaugurating the “Dark Ages.” ...

This is almost all utter nonsense, but I have to suppose that Amenábar [the director of Agora] believes it to be true.

...

The tale of a Christian destruction of the Great Library ”so often told, so perniciously persistent”is a tale about something that never happened .

So were mobs of Christians responsible for the destruction or is that just a modern myth?

Answer 1

The Library of Alexandria was destroyed/heavily damaged at least four times.

• 48 BC: Julius Caesar accidentally burns the library when he sets fire to his ships and the fire spreads from the docks. (Plutarch, Life of Caesar)
• 272 AD (roughly): Several areas of Alexandria (including the Library) are damaged when Emperor Aurelian suppresses Queen Zenobia's revolt. (per Ammianus Marcellinus)
• 391 AD: Emperor Theodosius I makes paganism illegal. Anti-Arian riots take place, and destroy many religious objects (Socrates of Constantinople, Historia Ecclesiastica), although I find it unclear whether the scrolls of knowledge in the Library were actually destroyed.
• 642 AD: The Muslim army captures Alexandria. ~500 years later, several accounts of the invasion mention the destruction of the Library and/or some or all of its contents by the order of Caliph Omar (such as Al-Qifti, History of Learned Men)

Yes, there were religion-based riots in 391 AD, and yes, things in the Serapeum were destroyed. Whether the destroyed items included the scrolls of the Library or only the religious artifacts, however, I'm unclear.