Eratosthenes was a native of Cyrene, on the south coast of Mediterranean Sea, and was only a few years younger than Archimedes. He spent many years of his early years in Athens and, when about forty, was invited by Ptolemy III of Egypt to come to Alexandria as tutor to his son and to serve as chief librarian at the University there. It is told that in old age, about 194 B.C., he became almost blind from ophthalmia and committed suicide by voluntary starvation.

Eratosthenes was singularly gifted in all the branches of knowledge of his time. He was distinguished as a mathematician, an astronomer, a geographer, a historian, a philosopher, a poet, and an athlete. It is said that the students at the University of Alexandria used to call him Pentathlus, the champion in five athletic sports. He was also called Beta, and some speculation has been offered as to the possible origin of this nickname. Some believed that it was because his broad and brilliant knowledge caused him to be looked upon as a second Plato. A less kind explanation is that, though he was gifted in many fields, he always failed to top his contemporaries in any one branch; in other words, he was always second best. Each of these explanations weakens somewhat when it is learned that a certain astronomer Apollonius (very likely Apollonius of Perga) was called Epsilon. Due to this, the historian James Gow has suggested that perhaps Beta and Epsilon arose simply from the Greek numbers (2 or 5) of certain offices or lecture rooms at the University particularly associated with the two men. On the other hand, Ptolemy Hephaestio claimed that Apollonius was called Epsilon because he studied the moon, of which “ e” was a symbol.

In arithmetic Eratosthenes is noted for the following device, known as the sieve, for finding all the prime numbers less than a given number.