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Pi has been fascinating people for thousands of years. The first recorded investigations of pi were from the Ancient Egyptians and Babylonians around 4000 years ago. The Babylonians approximated the value of pi to 3.125 by measuring the perimeter of a hexagon inscribed within a circle and estimating that a hexagon's perimeter was 24/25 of the circumference of a circle. The ancient Egyptians approximated pi with a value of 3.16045. The actual value of pi, to 5 decimal places, is 3.14159, which means that these approximations were within a couple of hundredths of the true value of pi. These early calculations were largely measurement based since these ancient civilizations used pi in their architecture. It is speculated that the Ancient Egyptians had mythology surrounding pi since the pyramids of Giza- highly spiritual structures- were actually based on pi. The ratio of the vertical height of the pyramids to the perimeter of their bases is equivalent to pi (Mometrix).

In 220 BC, Greek mathematician Archimedes invented a method to approximate pi. His method was the first recorded method of approximation that wasn't based on observing measurements. His method consisted of inscribing and circumscribing regular polygons without a circle and using the outside and inside polygon as the upper and lower bounds for his approximation of pi (See this page for more detail on his method). Archimedes approximated pi to 3.1418, which is accurate to the thousandths place (Encyclopaedia Britannica). Archimedes also proved that the area of a circle is equal to pi multiplied by the square of the circle's radius, which is an equation that was groundbreaking and is still essential in mathematics today.

Across the world in the third century, Chinese Mathematician Liu Hui used the same method that Archimedes used, along with a 96 sided polygon to estimate pi with accuracy to 4 decimal places. For hundreds of years, no new methods to calculate pi were established- mathematicians simply tried to improve on the accuracy of Archimedes' regular polygon method. That lasted until the end of the 17th century, when mathematicians began exploring the use of infinite series to calculate pi. Srinivasa Ramanujan, an Indian mathematician, explored these methods and many others during his life in the early 1900s. Ramanujan formulated hundreds of ways to calculate pi. His most efficient way is now used in computer algorithms (Guillen). Now computers are used in the calculation of pi and mathematicians have been able to approximate pi to 31 trillion digits.

In 1706 William Jones, who was a British mathematician, invented the symbol for pi that we still use today. Although it was William Jones who invented the symbol, it was the famous Swiss mathematician Leonhard Euler who made the symbol popular. The symbol is a letter in the Greek alphabet and is the first letter of the Greek words for periphery and perimeter- both of which connect to the meaning of pi (Mometrix).