Eratosthenes (l. c. 276-195 BCE) was a Greek astronomer, geographer, mathematician, and poet best known for being the first to calculate the circumference of the earth and its axial tilt. He is also recognized for his mathematical innovation, the Sieve of Eratosthenes, which identified prime numbers, and his position as head of the Library at Alexandria.

More about: Eratosthenes


  • 276 BCE - 195 BCE
    Life of Eratosthenes, ancient Greek Alexandrian scholar, native of Cyrene and one of the greatest geographers in antiquity.
  • c. 240 BCE
    Eratosthenes calculates the earth's cirumference based on the difference in shadows at midday at two different locations in Egypt.