People have been interested in circles for a long time. One can imagine early humans attaching a cosmic significance to circles. After all, the two greatest objects in the sky, the sun and the moon, are circles. We know that by at least 2000 BC, humans had discovered an important universal property of all circles. If you measure a circle's perimeter (circumference) and divide by its width (diameter) you get a number that is the same for all circles...