Thales (circa 600BC—roughly 50 years before Pythagoras, 200 years before Plato, and 300 years before Euclid) certainly knew and reasoned with the concept of a planar angle. Are there earlier historical references to angles in a mathematical sense? Or is the origin of the notion lost in the mists antiquity?

Thales (circa 600BC—roughly 50 years before Pythagoras, 200 years before Plato, and 300 years before Euclid) certainly knew and reasoned with the concept of a planar angle. Are there earlier historical references to angles in a mathematical sense? Or is the origin of the notion lost in the mists of antiquity?