Long before the European Enlightenment and the Darwinian revolution, which we often take to mark the birth of the modern revolt against religious explanations of the world, brave people doubted the power of the gods. Religion provoked skepticism in ancient Greece, and heretics argued that history must be understood as a result of human action rather than divine intervention. They devised theories of the cosmos based on matter, and notions of matter based on atoms. They developed mathematical tools that could be applied to the world around them, and tried to understand that world in material terms. Their skepticism left a rich legacy of literature, philosophy and science, and was defended by great writers like Epicurus, Lucretius, Cicero and Lucian. Tim Whitmarsh tells the story of the tension between orthodoxy and heresy with great panache, a story that ended--for the moment--with the imposition of Christianity on the Roman Empire in 313 CE.