On a dusty road in southern Italy, sometime in the early fifth century BCE, a small procession of young men walks behind an older figure. They are heading toward the city of Elea, a Greek colony on the Tyrrhenian coast. Trade ships move in the harbor; farmers bring goods into the market; priests tend to local shrines. The older man is not a politician, not a general, not a seer. He is a poet and a thinker, Parmenides of Elea, and the poem he has composed will strike at the heart of how human beings think about reality. Behind him, though they do not yet know it, trails a revolution in the very idea of what it means for something to “be.”