This biography introduces Eratosthenes whose mathematical approach opened new ways to describe and understand the world. Using mathematics to study the earth, Eratosthenes broke new ground. In his monumental three-volume Geographica, he took a global view of the world. With its title, he coined a new word, geography. His work in chronology, theater criticism, and as director of the Alexandrian library were among the Greeks’ valuable contributions to Western learning.