And yet the theory of retribution had not been without its influence upon Thucydides. It even forces the structure of his later books into the regularity of a tragedy, in which Athens is the protagonist, and a verse of Sophocles the theme. But his earlier and greater manner prevails, and from the study of his work the mind passes easily to the contemplation of the doom which awaited the destroyers of Athens, the monstrous tyrannies in Syracuse, and Lacedaemon's swift ruin. Another phase of the position of Tacitus deserves attention. It was a habit of writers of the eighteenth century, in treating of the vicissitudes of empires, to state one problem and solve another. The question asked was, "Is there a law regulating the fall of empires?"; but the question answered, satisfactorily or unsatisfactorily, was, "Is there a remedy?" Like the elder Cato, Tacitus seems in places to refer the ruin which he anticipated to Rome's departure from the austerity and simplicity of the early centuries. In the luxury of the Caesars he discerns but another condemnation of the policy of Caius Julius. The use which Gibbon has made of this argument is celebrated. In Gibbon's life, indeed, regret for the Empire, for the Rome of Trajan and of Marcus, exercises as strong a sway, artistically, as regret for the Republic exercises over the art and thought of Tacitus. Both desiderate a world which is not now, musing with fierce bitterness or cold resignation upon that which was once but is no longer. Both ponder the question, "How could the disaster have been averted? How could the decline of Rome have been stayed?" Tacitus is the greater poet--more penetrating in vision, a greater master of his medium, profounder in his insight into the human heart. But a common atmosphere of elegy pervades the work of both, and if Gibbon again and again forgets the inquiry with which he set out, the charm of his work gains thereby. A pensive melancholy akin to that of Petrarch's _Trionfi_, or the _Antiquités de Rome_ of Joachim du Bellay, redeems from monotony, by the emotion it communicates, the over-stately march of many a balanced period.[8] But it were as vain to seek in Tasso for a philosophic theory of the Crusades as seek in Gibbon a philosophic theory of the decline of empires.