Everybody knows the value of pi is 3.14…er, something, but how many people know where the ratio came from?

Actually, the ratio came from nature—it’s the ratio between the circumference of a circle and its diameter, and it was always there, just waiting to be discovered. But who discovered it? In honor of Pi Day, here’s a semi-brief history of how pi came to be known as 3.14(1592653589793238462643383279502884197169…and so on).

*Editor’s note: This article originally published in 2010. We’re rerunning it today in honor of Pi Day, 3/14. * *You may also want to check out our roundup of **10 surprisingly practical Raspberry Pi projects anybody can do*.

## The history lesson

It’s hard to pinpoint who, exactly, first became conscious of the constant ratio between the circumference of a circle and its diameter, though human civilizations seem to have been aware of it as early as 2550 BC.

The Great Pyramid at Giza, which was built between 2550 and 2500 BC, has a perimeter of 1760 cubits and a height of 280 cubits, which gives it a ratio of 1760/280, or approximately 2 times pi. (One cubit is about 18 inches, though it was measured by a person’s forearm length and thus varied from one person to another.) Egyptologists believe these proportions were chosen for symbolic reasons, but, of course, we can never be too sure.

The earliest textual evidence of pi dates back to 1900 BC; both the Babylonians and the Egyptians had a rough idea of the value. The Babylonians estimated pi to be about 25/8 (3.125), while the Egyptians estimated it to be about 256/81 (roughly 3.16).Archimedes didn’t calculate the exact value of pi, but rather came up with a very close approximation—he used 96-sided polygons to come up with a value that fell between 3.1408 and 3.14285.The Ancient Greek mathematician Archimedes of Syracuse (287-212 BC) is largely considered to be the first to calculate an accurate estimation of the value of pi. He accomplished this by finding the areas of two polygons: the polygon that was inscribed inside a circle, and the polygon in which a circle was circumscribed (see figure above, right).

Chinese mathematician Zhu Chongzhi (AD 429-500) used a similar method…