Eratosthenes Measures the Earth

In about 240 BC, the scholar Eratosthenes was the chief librarian of the Great Library of Alexandria, the ancient world's premier center of knowledge. He was a polymath, an expert in many fields, which earned him the nickname 'Pentathlos', like an athlete competing in five events. But his peers had another, less flattering name for him: 'Beta'. They considered him the second-best at everything he did. Summoned to Alexandria by the pharaoh Ptolemy III Euergetes, Eratosthenes had access to hundreds of thousands of papyrus scrolls containing reports from across the known world. It was in one of these scrolls that he found a peculiar observation, a puzzle that would lead him to his greatest achievement: measuring the world itself.