The Romans conquered most of the known world and detailed their conquests in calm, unapologetic histories. They were a supremely urbane people who longed poetically for the farming life. Valuing toughness and practicality in all things, they turned the love poem into a cynical rebuke and wrote tragedies in which the unfathomable actions of gods gave way to the staggering cruelties of man. As the empire slid into decay, Tacitus pulled back the curtain on the perverse intrigues of the emperors, and a Roman-educated Christian named Augustine recounted his spiritual awakening in what may be the...