Orosius expressly states that he saw the empty cases or shelves of the library twenty years after Theophilus, the uncle of St.Cyril, had procured from the Emperor Theodosius a rescript for its destruction.

Even had this once noble collection never endured such acts of violence, the mere wear and tear, and perhaps, I may add, the pilfering of a thousand years, would have diminished it sadly.
Though John, as the surname he received indicates, might rejoice in a superfluity of occupation, we may be certain that the care of a library of half a million books would transcend even his well-tried powers; and the cost of preserving and supporting it, that had demanded the ample resources of the Ptolemies and the Caesars, was beyond the means of a grammarian.

Nor is the time required for its combustion or destruction any indication of the extent of the collection.

Of all articles of fuel, parchment is, perhaps, the most wretched.

Paper and papyrus do excellently well as kindling-materials, but we may be sure that the bath-men of Alexandria did not resort to parchment so long as they could find any thing else, and of parchment a very large portion of these books was composed.
There can, then, be no more doubt that Omar did order the destruction of this library, under an impression of its uselessness or its irreligious tendency, than that the Crusaders burnt the library of Tripoli, fancifully said to have consisted of three million volumes.