Cornelius Tacitus was perhaps the greatest historian that the Roman world produced. Though his Annales (Annals, after A.D. 116) and Historiae (Histories, ca. A.D. 100-110) are among the most remarkable works of Latin prose, their extraordinary influence derives not from an agreeable style or from an uplifting theme, for his account of the loss of freedom under the Julio-Claudian and Flavian emperors is grim and depressing, but from the psychological penetration, acute political analysis, moral grandeur, and literary genius that have dazzled his readers for five centuries.

What is known of the life of Tacitus comes from his writings--especially his biography of his father-in-law, Agricola. There are almost no contemporary references to him save the correspondence with his friend Pliny. Scholars cannot even be certain whether Tacitus's praenomen was Gaius or Publius.

Early in the reign of Nero (A.D. 54-68), Tacitus was born into a prominent...