A quibble, I know... but nobody "invented" Pi , its not something to be invented. Now , who was the first to UNDERSTAND Pi and to figure its parameters we'll probably never know but its approximate value has been know and used for a very long time : ...."The Egyptian scribe Ahmes wrote the oldest known text to give an approximate value for Pi, citing a Middle Kingdom papyrus"...... ." "By 2000 B.C., Babylonians established the constant circle ratio as 3-1/8 or 3.125. The ancient Egyptians arrived at a slightly different value of 3-1/7 or 3.143"...... not far off and considering, not too bad.