Eratosthenes
Assuming that Alexandria was due north of Syene he concluded that the distance from Alexandria to Syene must be 1/50 of the total circumference of the Earth (360 degrees). His estimated distance between the cities was 5000 stadia () by estimating the time that he had taken to travel from Syene to Alexandria by camel. He rounded the result to a final value of 700 stadia per degree, which implies a circumference of 250,000 stadia. The exact size of the stadion he used is frequently argued. The common Attic stadium was about , which would imply a circumference of , which is  different from the currently accepted circumference of the Earth (). The method is an early application of trigonometry in the measurement science of geodesy.