Was the library of Alexandria burnt to the ground by the Christian crusaders?

I cannot for the life of me remember whether it was Ceaser's conquest of Egypt that undid the library, or burned by edict of the catholic papacy for holding heretical texts during the crusades. Please Y!A, re-enlighten me.
Update: uggh, the anti-intellectualism from slam-man's answer makes me cringe, everyone else, thanks for the responses.
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