Eratosthenes was an important mathematical figure of ancient Greece. Among his accomplishments was the accurate measurement of the earth's circumference. He also wrote works on mathematics, geography, philosophy, and astronomy. Although many of his works have been lost, historians have uncovered a substantial amount of information about important events in his life and his accomplishments.

Q: Where were you born and where did you grow up?

A: I was born in Cyrene, Greece (which is present-day Libya, in South Africa), in 276 B.C. Both of my parents were Greek and there, on the coast of Africa, I grew up.

Q: Did you have any nicknames growing up?

A: I did have one; my friends called me Beta, which is the second letter of the Greek alphabet. They teased with me, saying I fell just short of first place (which was occupied by Archimedes). Later on in my life, I received the nickname Pentathlos. It's funny, because literally this word refers to an athlete that participated in 5 sporting events, but eventually was used to describe someone who was well-rounded, or good at several different things.

Q: What was your childhood like?

A: My parents told me that I had always been a curious baby, sticking my hands into new and foreign objects, typical baby behavior. But as I grew older, I asked thousands of questions that nobody could answer. I was very fascinated by the sky, because it was something that I could not reach up and touch. I wondered how far away the sun was, what it was made of, where the winds came from, and how the stars moved. When I was about six years of age, I began to go to the gymnasium, which is a school. I learned reading, writing, arithmetic, music, and poetry. I was very strong in math but geography was by far my favorite subject.

Q: What were the turning points of your life?

A: Well, I sailed to Athens to study there, and somehow made myself so known in several fields, that Ptolemy III of Egypt invited me to Alexandria. There, I tutored his son Philopater, and became the librarian for the great Alexandrian University. That was something that completely changed my life; it was the most exciting place to be, because it was considered the center of all learning. The library and museum were the best in the world. In the library at Alexandria, there were seven hundred thousand papyrus scrolls and forty librarians.

Q: What were you major accomplishments?

A: I created a sieve that determines prime numbers up to any limit. This sieve was important in number research theory. I also was able to accurately measure the circumference of the Earth. And I, being the list maker that I am, worked on figuring out the dates of literary and political events, a list called a chronology. I wrote some books as well, one on comedy, one on history, and one on the constellations.

Q: How did you measure the circumference of the Earth?

A: Well in order to find a circumference, I made two assumptions: that the earth was round and that the sun's rays were essentially parallel because the sun was so far away. I imagined that a section of the earth ran from Alexandria to Syene, and if I could figure out the distance, and measure the inside angle of the section they created, I would be able to calculate the earth's circumference. I picked Syene because I heard from a caravan passing through Alexandria that on the twenty-first day of June at precisely midday, the sun would shine directly down a certain well in Syene, lighting up the well but casting no shadows on its walls. I supposed the earth was like a grapefruit: if I could find the distance of one section of the arc, I could find out how many of these same-size sections it would take to make up the whole grapefruit. Since a circle is made up of 360 degrees, with the inside angle I could figure out how many inside angles make up 360, and then the whole circumference.

The circumference of the earth calculated by Eratosthenes was only two hundred miles off from the modern day figure, and considering the magnitude of the numbers, it can be considered the first accurate measurement. After his discovery, he provided the first mathematically based map of the world. His Geographica, geography book of the world, was finally complete.

Work Cited

Bendwick, Jeanne and Lavin, Marcia. Mathematics Illustrated Dictionary. New York: McGraw-Hill Book Company, 1965.


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Hogben, Lancelot. Mathematics for the Million. Rendlesham: Merlin Press, 1989.

Lasky, Kathryn. The Librarian Who Measured the Earth. Boston: Little Brown and Company, 1994.

O'Conner, J. J. and Robertson, E.F. “Eratosthenes of Cyrene”. School for Mathematics and Statistics. University of St. Andrews, Scotland, 1999.

Rogers, Al. “Eratosthenes in Schools”.

Smith, D. E. History of Mathematics. New York: Dover Publications Inc, 1998

Weisstein, Eric W. “Eratosthenes of Cyrene”.