“Cosmos” is one of the most important and most deeply misunderstood words in our vocabulary. In common use, it designates the stars and planets beyond Earth, realms accessible only by telescopes or the most futuristic of technologies. But the complex history of this ancient word suggests that it has much more to teach us—indeed, that we need it now more than ever, for popular usage masks its long history as humanity’s oldest ecological vision of our planet. In ancient Greece, “_kosmos_” meant not “the universe”—for this the Greeks used “_τò πᾶν_,” “the all”—but rather, the universe comprehended as a unified system that was both ordered and beautiful. How, they asked, did this this system come into being? Of what did it consist, what was its fate? Their answers elaborated a plethora of possibilities that initiated what we now call “science.” _Kosmoi_ were variously imagined as finite or infinite; designed and fated, or bubbling up by chance; single and identical with the universe, or many coexisting in a pluriverse, or perhaps rising, flourishing, and dying in a succession of rebirths—but in all cases, the ancient Greeks imagined their _kosmoi_ arising from some prior state of “chaos,” not, as in the Christian...