They didn’t even have access to algebraic notation (IIRC, an innovation of the Islamic Golden Age, a result of cross-pollinating Greek geometry with Indian arithmetic). So the groundbreaking material was that famous diagram of a right triangle with squares constructed on each side.

Interestingly, there is no actual reference to Pythagoras for this discovery until 5 centuries later, by Greek authors Plutarch and Cicero attributing this theorem specifically to Pythagoras.

However, Pythagoras’ Theorem is often linked to the Babylonians. There are implications of the theory on a fragment of a clay tablet from Babylonia in the Plimpton 322, dating back to approximately 1800 BCE.