Pythagoras was an Ionian Greek born on the island of Samos, probably about 570 BCE. His dislike of the policies of the Samian tyrant Polycrates caused him to immigrate to Crotona in southern Italy. There he founded a society with religious and political, as well as philosophical, aims that gained power in the city and considerably extended its influence over the surrounding area. A certain Cylon, however, stirred up a revolt against the society in which a number of its leading members were killed, and Pythagoras retired to Metapontum. The community recovered its influence until a more serious persecution took place in the middle of the fifth century, from which the survivors scattered to various parts of the Greek world—notably Thebes, Phleius, and Tarentum. In these places "they preserved their original ways and their science, although the sect was dwindling, until, not ignobly, they...