We are in thrall of new technologies. Biotechnology, nanotechnology, information technology… New advances boggle our minds. But how many of us would know how to sow corn, harvest it, grind it into flour, and make something edible with it? Or shear a few sheep, spin wool, and knit anything useful out of it? Or wash some laundry with ashes? Technologies known to almost everyone a few generations back are as remote as those needed for mass manufacturing of flying saucers. Although most of them have been written up many times over, few of us would know how to find the relevant books before they fall prey to mice. Or how to interpret anything we find in them. Or how to use the knowledge gained by reading. The collapse of our civilization would thus bring us not a few hundred years back, but a few thousand at least. And we would find ourselves dreaming of the technological advances of Greece and Rome of old. They would be out of our fretful reach for centuries ahead.