Ancient Greek mathematicians used a physical string to calculate the Earth's circumference
Around 240 BCE, Eratosthenes calculated the Earth's size by measuring shadows in two cities and hiring professional pacers to physically walk the distance between them using knotted ropes.
Eratosthenes determined the Earth's circumference with incredible precision by comparing the angles of shadows in Alexandria and Syene. To find the exact distance between these cities, he utilized professional bematists, or step-measurers, who stretched knotted ropes to ensure every pace was uniform.
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