The symbol π was first proposed by the Welsh mathematician William Jones in 1706.Pi was approximated by almost all ancient civilizations including Indians who have described about this in Vedic mathematics. The earliest documented conscious use of a precise approximation for the length of a circumference with respect to its radius is of 3+1/7 in the designs of the Old Kingdom pyramids in Egypt. 

The fact that the ratio of the circumference to the diameter of a circle is the same for all circles, and that it is slightly more than 3, was well known to ancient Egyptian, Babylonian, Indian and Greek geometers. The earliest known approximations date from around 1900- 1680 BC. They are 25/8 by ancient Babylonians and 256/81 by ancient Egyptians, both within 1% of the true value.

The Indian astronomer Yajnavalkya gave astronomical calculations in the book on Vedic Maths titled “Shatapatha Brahmana” (c. 9th century BC) that led to an approximation of pi = 339/108 = 3.1389.. The Books of Kings (600 BC) appears to suggest π = 3, which is markedly worse than other estimates available at the time, although the interpretation of the passage is disputed. Archimedes of Syracruse (287-212 BC) was the first to estimate π rigorously. Archimedes's results rested upon approximating the area of a circle based on the area of a regular polygon inscribed within the circle and the area of a regular polygon within which the circle was circumscribed. Starting with a hexagon, he worked all the way up to a polygon with 96 sides and based this he proved that 223/71 < π < 22/7. Taking the average of these values yields 3.1419.

In the subsequent centuries, most significant development took place in India and China. In 5th century CE, Indian mathematician Aryabhata is credited to have made the closest approximation for pi as 3.1416. He was the first one to pronounce that it is an approximation and the original value is irrational.

Around 480 AD, the Chinese mathematician Zu Chongzhi gave the approximation π = 355/113, and showed that 3.1415926 < π < 3.1415927. Zu's value of pi is precise to 8 decimal places. No mathematician since his time, computed a value this precise until another 1000 years. 

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