"How do you find the holy grail of mathematics? 
--You start with a circle, which is the easiest geometric shape to draw
(just fix one end of a string in place and swing the other end around
it, inscribing a circle).
--Then measure the circle’s perimeter (also
known as the circumference) and the distance across its widest point
(the diameter).
--Divide the circumference by the diameter—and you have
that well-known but eternally daunting number, π, or pi, which has a value of 3.14159265…
That is part of the mystique of pi: Whatever the size of the circle, the value remains the same (what mathematicians call a “constant”). Unfortunately, pi
is also “irrational,” meaning that it is impossible to calculate its
value completely; the decimals go on forever without regular repetition.
Calculating the value of pi has been a puzzle for millennia. One of the earliest implied values is given in a Biblical passage describing the construction of a huge basin for Solomon’s Temple: “Then [Hiram of Tyre] made the molten sea; it was round, ten cubits from brim to brim, and five cubits high. A line of thirty cubits would encircle it completely” (1 Kings 7:23). In other words, pi = 30÷10 or 3.
The Temple craftsmen obviously obtained these numbers through direct
measurement—perhaps using a rope—and they came up with a simple
approximation of pi.
More than a thousand years earlier, the Sumerians
had developed a mathematical method for measuring the dimensions of
circles, that of inscribed equilateral polygons (a geometric shape with
three or more straight sides). The ancient Sumerians realized that the
perimeter of a polygon inscribed in a circle would always be slightly
smaller than the circle’s circumference. This allowed them to make a
fairly accurate measurement of a curved line, which is almost impossible
to do with ordinary measuring devices." BiblicalArchaeology