How long is eternity?

Henry Schlieman, nineteenth-century genius, discoverer of the ruins of of the ancient city of troy, answered his son's question with a sweep of his hand:

"Picture a wall of marble ten yards high and ten yards wide stretching all the way from here in Athens to the little Greek harbor town of Piraeus, there in the distance.

Now imagine a bird coming along once every thousand years to draw a silken scarf along the entire length of this gigantic slab of stone.

By the time the friction will have worn the wall of marble down to the thickness of a mere sliver, one second of eternity will have passed."

From the book 'Starwatch,' by Ben Mayer, A.R.C.A.