Archimedes (287-212 B.C.) was the Greek mathematician and inventor who articulated many of the principles you learned in high school, like how you can use pi to to calculate the area of a circle, and how the volume of a sphere is always two-thirds the volume of the cylinder it fits inside.  Archimedes showed how an object submerged in water loses weight equal to the water it displaces, and he also may have invented the compound pulley.

Scientists have discovered another of his writings.  Using X-ray technology, they've been able able coax into the light of day miniscule traces of ink (which luckily contains iron) from Archimedes' work, the palimpsest, which was copied down in the tenth century, but later erased and written over.  The X-rays of the pages reveal the original work underneath.