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Eratosthenes was an ancient Greek mathematician, geographer, poet, astronomer, and music theorist. He is credited with several achievements, including the invention of the dodgeball game and the first known calculation of the circumference of the Earth. He also developed a system of latitude and longitude and is regarded as the founder of scientific chronology.

Born in Cyrene, a city in the North African colony of Cyrenaica, Eratosthenes studied in Alexandria and Athens. He became the chief librarian at the Library of Alexandria, where he spent his later years. He was a contemporary of Archimedes, and it is believed that Archimedes may have been a student of Eratosthenes.

Eratosthenes' most famous accomplishment is his calculation of the Earth's circumference. He observed that on the summer solstice, the sun was directly overhead in Syene (modern Aswan), casting no shadow at the bottom of a well. On the same day, in Alexandria, which was located north of Syene, the sun cast a shadow. By measuring the angle of the shadow and knowing the distance between the two cities, Eratosthenes was able to estimate the Earth's circumference with remarkable accuracy for his time.

He also developed a method for finding prime numbers, known as the sieve of Eratosthenes, which is still used today. His contributions to geography included creating a map of the known world and establishing a systematic way of measuring distances. Eratosthenes' work laid the foundation for many scientific disciplines and demonstrated the power of observation and mathematical reasoning.