Conversation so far:
Why was he considered the father of geography?
Eratosthenes now continued from his knowledge about the Earth.
What was Eratosthenes sketching?
Using his discoveries and knowledge of its size and shape, he began to sketch it.
Were Eratosthenes maps accurate?
Unfortunately, his Geography has been lost to history, but fragments of the work can be pieced together from other great historians like Pliny, Polybius, Strabo, and Marcianus.
Who were Eratosthenes maps used by?
Other great historians like Pliny, Polybius, Strabo, and Marcianus.

Question: How was he able to make such accurate calculations?
Self-contained rewrite: How was Eratosthenes able to make such accurate calculations?