By increasing the number of sides of the polygons, the perimeters become closer in length to the circumference of the circle. Approximating Pi Infinite Secrets homepage ...

Specifically, he determined that pi was less than 3 1/7 but greater than 3 10/71. In the decimal notation we use today, this translates to 3.1429 to 3.1408. That's pretty close to the known value ...