Eratosthenes has been thoroughly debunked by the FE Awakening. His calculation also works if the sun is local at about 3K miles away. He also did not take into account refraction or atmospheric lensing. Also there was no way for him to prove that he was in the same latitude or time since there was no instant communication between the two cities. https://www.youtube.com/results?q=eratosthenes+was+wrong+debunked