There are some, King Gelon, who think that the number of the sand is infinite. I will try to show you that some of the numbers I have named exceed not only the number of the sand that would fill the Earth, but also that of the sand that would fill the universe. — Archimedes, The Sand Reckoner, letter to King Gelon The Sand Reckoner is a letter to Gelon, son of King Hiero, and the only book by Archimedes written for a reader who was not a mathematician. The problem is to prove that there is a number larger than the quantity of grains of sand needed to fill the whole universe.