Pythagoras monument. View of a statue of the Ancient Greek mathematician and philosopher Pythagoras (c.580-500 BC). Pythagoras made important developments in astronomy, mathematics, and the theory of music. He was the founder of the religious and scientific society called the Pythagoreans and is best known for the Pythagorean theorem that describes the relationship between the sides of a right-angled triangle. Photographed by the harbour in Pythagoreio, Samos, Greek Islands, where Pythagoras was born.