6821
As far back as the 3rd century BC , Eratosthenes had correctly computed the circumference of the Earth by using simple geometry and studying the shadows cast by objects at two remote locations .
 Eratosthenes
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Eratosthenes