The Pythagorean Theorem, which is often associated with Pythagoras, is actually documented on an ancient Babylonian clay tablet known as IM 67118, predating Pythagoras by more than a millennium. This tablet, believed to be used for instructional purposes, dates back to 1770 BCE, centuries before Pythagoras' birth around 570 BCE.
In another tablet from approximately 1800-1600 BCE, there are inscribed squares with labeled triangles inside. These inscriptions, using the base 60 counting system employed by ancient Babylonians, reveal their knowledge of the principles that would later be known as the Pythagorean theorem, albeit without that specific name.
Mathematician Bruce Ratner, in a paper on the subject, concludes, "The Babylonians knew the relationship between the length of the diagonal of a square and its side: d=square root of 2. This was probably the first number known to be irrational. However, this, in turn, means that they were familiar with the Pythagorean Theorem – or, at the very least, with its special case for the diagonal of a square (d2 = a2 + a2 = 2a2) – more than a thousand years before the great sage for whom it was named."
So, why is the theorem attributed to Pythagoras? The lack of surviving original writings from Pythagoras himself plays a role. Our knowledge of him is primarily passed down through others, particularly the Pythagoreans, a group connected to the school he established in what is now southern Italy, known as the Semicircle of Pythagoras. While this school was secretive, the knowledge gained there or developed was disseminated and often ascribed to Pythagoras himself.
"One reason for the rarity of Pythagoras' original sources was that Pythagorean knowledge was passed on from one generation to the next by word of mouth, as writing material was scarce," Ratner explained. "Moreover, out of respect for their leader, many of the discoveries made by the Pythagoreans were attributed to Pythagoras himself; this would account for the term ‘Pythagoras' Theorem’."
Although Pythagoras didn't originate the theory, his school played a pivotal role in popularizing it, and it remained associated with his name for millennia to come.