As is true of another enormously charismatic and influential ancient Greek philosopher -- Socrates -- Pythagoras seems to have written nothing; certainly nothing reliably attributed to him survives. So, as in the case of Socrates, information about his life and works must be gathered from later sources, many of which are worthless historically and none of which merits complete trust. The best evidence is from nearly two centuries or more after Pythagoras's death and is thus already deeply infected by the growth of Pythagorean legend; later sources become ever more contradictory and tendentious. Worse, some of Pythagoras's earliest biographers -- Aristoxenus, Dicaearchus, Neanthes, and Timaeus -- freely distorted whenever they saw fit.

Perhaps the most reliable biographical testimony comes from Aristotle in his fourth-century-B.C. On the Pythagoreans, which survives only in fragmentary form. Even Aristotle's information was tainted: Aelianus in Varia Historia reports Aristotle as saying...