There was a time in the ancient world - a very long time - in which the central cultural problem must have seemed an inexhaustible outpouring of books. Where to put them all? How to organize them on the groaning shelves? How to hold the profusion of knowledge in one's head? The loss of this plenitude would have been virtually inconceivable to anyone living in its midst. Then, not all at once but with the cumulative force of a mass extinction, the whole enterprise came to an end. What looked stable turned out to be fragile, and what had seemed for all time was only for the time being.