March 14th, 2017

Today is 'Pi Day', as March 14th can be shorthanded 3.14. Pi has been known since the 2nd millennium BC, and possibly earlier. Throughout antiquity, pi had no symbol, and was usually written as a fraction or root that roughly equalled pi (i.e. 25/8, or the square root of 10). The Greek letter π was first used by Welsh mathematician William Jones in 1706 to denote the constant. Jones chose this letter as an abbreviation for the Greek word περίμετρος, meaning perimeter. Needless to say, the trend stuck.

Bonus:

Since the discovery of pi there has been a tireless effort to calculate as many decimal places as possible. The progress was slow initially - 2000 years after being discovered only 7 decimal places were known - but accelerated tremendously with the advent of computers in the 1950s. As of 2016, pi is known to 22,459,157,718,361 decimal places.

-E