After its rediscovery in 1417, Lucretius's Epicurean didactic poem De Rerum Natura threatened to supply radicals and atheists with the one weapon unbelief had lacked in the Middle Ages: good answers. Scholars could now challenge Christian patterns of thought by employing the theory of atomistic physics, a sophisticated system that explained natural phenomena without appeal to divine participation, and argued powerfully against the immortality of the soul, the afterlife, and a creator God.

Ada Palmer explores how Renaissance readers, such as Machiavelli, Pomponio Leto, and...