Pi is the first useful everyday number discovered in ancient times. Pi has many practical uses when determining measurements of curved things (most of nature). It is rare to find a river that travels in exactly a straight line. Or to find an exactly straight coast line is also rare. How many hills look like a box? You see my point.
In more advanced mathematics you find the shortest distance between two points on out planet is not a straight line but a curve. In space the shortest distance between two points (time-wise) is actually a spiral. Truly fascinating how curves abound and how much pi helps us to calculate and understand them.