Monument to Pythagoras. Monument to the Greek philosopher Pythagoras (about 580-496 B.C.) in the harbour of Pythagorio, Samos, Greece. The monument is of Pythagoras as part of a right- angle triangle. Pythagoras taught that the squared hypotenuse length of a right-angle triangle is equal to the sum of the squares of the other two sides. This is known as Pythagoras' theorem and it is for this that he is best known. As well as being a philosopher and a mathematician, Pythagoras was also an astronomer. He taught that the Earth was spherical, and that the morning and evening stars were the planet Venus.