As of today, no primary source exists which discusses exactly what happened. For being such an important wonder of the ancient world, we actually don’t know that much about the Great Library in general.

What we do know is that the Great Library was known far and wide; they sought to obtain a copy of every book and manuscript in existence…. sometimes willfully, other times not. Sometimes books were purchased. Sometimes they were confiscated. Other times, they were borrowed, copied and returned. People form the far reaches of the world were encouraged to come to Alexandria and bring their literature. It was a place of learning and culture.

Various historians and scholars offer different versions on the Great Library’s destruction.

In 48 B.C.E. when G. Julius Caesar was under seize by the Egyptian Army while in Alexandria, he burned the Egyptian fleet in the harbor, and also his own ships to keep them all from being captured and used against him. Some nearby buildings caught on fire as a result… including the Great Library. The extent of the damage is not really known, however it wasn’t so bad as the Library being completely destroyed. It was probably bad enough however.

In 270 C.E., Queen Zenobia of Palmyra launched an invasion of the Eastern Roman Empire in which she annexed Egypt away from Rome and put it under her control. The Romans retaliated, and in 273 the Roman Emperor Aurelian destroyed a large portion of Alexandria during the re-conquest. The Library seems to have been damaged then as well. Again, it isn’t really known just how much damage there was.

In 391 C.E., the Roman Emperor Theodosius declared Christianity to be the only legal religion of Rome and that all pagan temples/shrines were to be destroyed. This included a big push to shut down pagan centers of learning for science, philosophy, mathematics, etc. which were typically run by Greeks. The Great Library was an unfortunate victim of this very ignorant purge... Religious fanatics pretty much destroyed what was left. Although by this time, the Library barely housed any books at all and was just a mere shell of its former self, its “golden age” long-gone.

Islamic scholars claim that the Great Library was still around (at least in some form) when the Umar Caliphate from Mecca conquered Alexandria in 641 C.E., and then it was burned after the conquest.

There doesn’t seem to be any real hard-and-fast date for when the Library ceased to exist. Though it does appear to have suffered a long, slow decline for various reasons.

In 2002, the Bibliotheca Alexandrina opened in Alexandria. This is a research library and cultural center created in commemoration of the old Great Library with the intention of turning Alexandria into a city of world-renowned learning once again. The Bibliotheca Alexandrina houses the world’s largest digital collection of historical manuscripts. It has shelf-space for 8 million books and the main reading room covers 220,000 square feet.