We will probably never know who discovered pi, or that the ratio of the circumference of a circle to its diameter is a constant. The search for that constant, also known as pi, goes back nearly 4,000 years, to the Egyptians and Babylonians.
The earliest recorded example of the formula for the area of a circle dates back to an Egyptian papyrus from about 1650 B.C. It gives the value of pi as (16/9)2, which is approximately equal to 3.1605. It is not known what method of calculation the early Egyptians used.
The ancient Greeks continued the search for pi by inscribing polygons within a circle, reasoning that the area of a polygon with many sides closely approximates the area of the circle circumscribing it. Archimedes of Syracuse both inscribed and circumscribed a circle with polygons with increasing numbers of sides. By calculating the perimeters of two 96-sided polygons, he showed that pi is greater than 223/71, but less than 22/7, or between 3.1408 and 3.1429. Over the centuries, mathematicians have developed more and more sophisticated methods of approximating the value of pi. As of today, the value of pi had been calculated to over 22 trillion digits.