Question: when was the library of alexandria burned down
Answer: Ancient and modern sources identify four possible occasions for the partial or complete destruction of the Library of Alexandria : Julius Caesar 's fire during his civil war in 48 BC ; the attack of Aurelian in AD 270 -- 275 ; the decree of Coptic Christian pope Theophilus of Alexandria in AD 391 ; and the Muslim conquest of Egypt in ( or after ) AD 642 .