ca. 285-ca. 195 B.C.
Eratosthenes was a versatile scholar whose work spanned a wide range of fields, including mathematics, geography, philosophy, poetry, and literary criticism. Born in the North African city of Cyrene, he lived in Athens for several years before accepting the offer of the Egyptian ruler Ptolemy III to become tutor to the royal family and head of the famous Library at Alexandria. Although most of his original writings have been lost, his extensive scholarship is reported by many prominent ancient authors, including the Greek geographer Strabo and the Roman historian Suetonius.
Eratosthenes is best known for his work in mathematics, geography, and chronology—the arrangement of events in time. He calculated the circumference of the earth more accurately than anyone before him, and he invented a method for identifying prime numbers. As a chronologist, Eratosthenes was the first to attempt to establish scientifically the dates of important political and historical events. He compiled a system of dating based on the lists of winners of the Olympic Games, and he began a project to replace the largely mythical chronology of prehistoric events with one that began with the fall of Troy. He is also considered to be the first systematic geographer. His three-volume work titled Geographica described the cultural and social development of various lands as well as their size, location, and physical features.
Among the scholars of Alexandria, Eratosthenes was sometimes criticized for being an “all-rounder” and for not concentrating on one subject. However, the brilliant Greek mathematician Archimedes accepted Eratosthenes as an equal in the field of mathematics, and Eratosthenes was considered the authority on geography and chronology by later Greek scholars. (See also Philosophy, Greek and Hellenistic; Ptolemaic dynasty.)