QUOTE : A slave was cheaper than a mule. Slavery, despicable topic, rarely appeared in poetry or onstage or in the paintings that decorated urns and walls. Philosophers ignored it, except to confirm it as the natural fate of inferior beings, and to sound the alarm. Watch out, warned Plato. Slaves, he said, unavoidably hate their owners and only constant vigilance can keep them from murdering us all. And Aristotle maintained that military training for the citizenry was crucial, given the climate of insecurity.