"Eratosthenes... knew that the Sun was straight overhead in... Syene at noon on the , but that it was 7.2 degrees south of straight overhead in , located 794 kilometers farther north. He concluded... 794 kilometers corresponded to 7.2 degrees out of the 360 degrees... around Earth's circumference, so that the circumference must be 794 km x 360°/7.2°≈39,700 km... remarkably close to the modern value of 40,000 km. Amusingly Christopher Columbus totally bungled this... confusing Arabic miles with Italian miles..."