Mathematicians tried to figure out what the number actually was. Archimedes famously approximated pi by drawing regular 96-gons (polygons with 96 sides) inside and outside of a circle to get as close as possible to the actual measure of the circumference of the circle. He figured out that pi is between 223/71 and 22/7.
Since pi is irrational, it can't be written as a fraction, and its decimal form goes on forever without repeating. We're still finding digits to pi--and we always will be!
Here's a musical interpretation of pi to celebrate pi day: http://www.youtube.com/watch?v=iOjsRyxL7Rs. Amazingly, it sounds pretty good!