How was the irrational number pi invented or how did man reach upon it? I have studied elementary calculus to understand the basic kinematics. Infact I know only the formulae to find for integration and derivative of some standard functions. The limits and such things weren't taught to me. It will be taught a year later. From this knowledge I myself proved the area of a circle and surface area of sphere, cylinder and cone and also their volume. But in finding the circumference of the circle, the formula that circumference of a circle is 2pi*r was uses. However I thought of a lot of ways but still cannot reach or use calculus to verify the formula for the circumference of a circle. I also felt the number pi like something heavenly and couldn't find any property in a curve which could have led to its invention. Is this because my present information on the subject is not sufficient or can I reach pi just from this information?