Where did pi come from?

The concept of the mathematical constant pi dates back approximately 4000 years to ancient Mesopotamia. Babylonian mathematicians found that the area of a circle was figured by taking the square of the radius, multiplied by their closest approximation of pi, which was 3.

The name pi came into use alongside the Greek character pi in the early 18th century, when British mathematician William Jones used the symbol to denote the ratio of a circle's circumference to its diameter. Over the millennia, the understanding and definition of pi has improved, and contemporary supercomputers can compute pi to over 10 trillion digits.