In a quiet corner of the Roman Empire sometime in the late second or early third century of our era, a physician sits at a wooden table, scratching notes onto a wax tablet by lamplight. Around him the house is dark; outside, the city is sleeping. On the shelves behind him are scrolls by Plato, Aristotle, Epicurus, Chrysippus, Hippocrates. He has read them all, argued with them in his mind, and found in each something impressive and something unproven. Tonight he is trying to do something different. Not to build yet another doctrine about the soul or the gods or the best life, but to catalogue the ways in which any such doctrine can be unsettled. His name is Sextus Empiricus, and though he writes in an age of worn-out certainties and competing cults, what he sets down will become one of the most powerful handbooks of doubt ever composed.

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