"Eratosthenes had the idea that, if he could measure the angle of the shadow in

"Eratosthenes had the idea that, if he could measure the angle of the shadow in alexandria and knew the distance between siena and alexandria, could calculate the circumference of the earth. For that, he hired a "bematist", a person trained to measure distances by walking with regular steps, who estimated the distance between the two cities at 5.040 stadiums, an ancient unit of measurement."