But again, the symbol isn't the math. We're actually talking about "that which cannot be designated". And it was certainly discovered if you're taking the the invented-discovered dichotomy ontology. Yes, the greek symbol pi was invented but it wasn't "created to exactly name" the number, it was a greek letter first: it's a cultural thing that pi is ONLY used for pi, many constants have symbols often used as variables, like permitivity uses mu Newton's gravitational constant is G (also used to represent Fourier transforms of arbitrary function, g.)
Anyway, the symbol isn't the math, as previously commented by another poster.
The circle was the thing invented (likely as an idealization of the observation of circle-like shapes and dynamics) and the ratio between it's diameter and it's circumference is the thing that was discovered about it... but the discovery goes beyond basic geometry, it has implications for a Euclidian universe in which Gauss's law (and it's generalization) is valid. Pi tends to crop up in lots of other places in physics, too.