OT - That's not right, about Alexandria
First, the Alexandrian Library was not the single portal to written knowledge, there were other great libraries at the time. Ptolemy II had the ambition that the library should contain a *copy* of every book that existed, not that it should contain all the world's books, His son Ptolemy III is alleged to have been an obsessive collector for the library, borrowing other collections and returning only copies.
Secondly, it did not all burn down at once. Julius Caesar "liberated" a good deal of it, but much remained in the city after that. Its eventual fate is unknown, and thus unlikely to have been any one cataclysmic destruction. The myth that it was finally destroyed by the Arab conquerors in the 7th century CE is also discredited.