Born in Cyrene and educated by the poet Callimachus, Erastothenes became the head of the library in Alexandria at about the age of 36.
He managed to measure the circumference of the earth almost exactly by astronomical calculations and wrote a book on 675 stars. He also wrote about geography and calculated the earths tilt and was the first to divide Earth into longitudes and latitudes.
Erastothenes tried to measure the distances between various countries and cities, a project which was to be completed by Hipparchus.
He was also called Mr. Beta since he always came second as far as his contributions to science were concerned, since he was a contemporary and friend of the great Archimedes.
When he became blind, he starved himself to death.