Pythagoras (c.580-c.490 BC), Ancient Greek philosopher, with Egyptian priests. Pythagoras is thought to have studied in Egypt for 21 years. It is said that it was there that he learnt the proof involving triangles that is now called Pythagoras' Theorem. He later established an eccentric religious community in southern Italy based on the mystical belief that insall is numberins. Artwork from the 19th century book Vies des Savants Illustres.