unbounded; and when Nero became Emperor at the age of seventeen, Seneca, in conjunction with his close friend, Afranius Burrus, commander of the imperial guards, became practically the administrator of the Empire. His philosophy was not one which rejected wealth or power; a fortune of three million pounds may have been amassed without absolute dishonesty, or even forced upon him, as he pleads himself, by the lavish generosity of his pupil; but there can be no doubt that in indulging the weaknesses and passions of Nero, Seneca went far beyond the limits, not only of honour, but of ordinary prudence. The mild and enlightened administration of the earlier years of the new reign, the famous _quinquennium Neronis_, which was looked back to afterwards as a sort of brief golden age, may indeed be ascribed largely to Seneca's influence; but this influence was based on an excessive indulgence of Nero's caprices, which soon worked out its own punishment. His consent to the murder of Agrippina was the death-blow to his influence for good, or to any self-respect that he may till then have retained; the death of Burrus left him without support; and, by retiring into private life and formally offering to make over his whole fortune to the Emperor, he did not long delay his fate. In the year 65, on the pretext of complicity in the conspiracy of Piso, he was commanded to commit suicide, and obeyed with that strange mixture of helplessness and heroism with which the orders of the master of the world were then accepted as a sort of inevitable law of nature. The philosophical writings of Seneca were extremely voluminous; and though a large number of them are lost, he is still one of the bulkiest of ancient authors. They fall into three main groups: formal treatises on ethics; moral letters (_epistolae morales_), dealing in a less continuous way with the same general range of subjects; and writings on natural philosophy, from the point of view of the Stoical system. The whole of these are, however, animated by the same spirit; to the Stoical philosophy, physics were merely a branch of ethics, and a study to be pursued for the sake of moral edification, not of reaching truth by accurate observation or research. The discussions of natural phenomena are mere texts for religious meditations; and though the eight books of _Naturales Quaestiones_ were used as a text-book of physical science in the Middle Ages, they are totally without any scientific value. So, too, the twenty books of moral letters, nominally addressed to Lucilius, the procurator of Sicily, merely represent a slight variation of method from the more formal treatises, _On Anger, On Clemency, On Consolation, On Peace of Mind, On the Shortness of Life, On Giving and Receiving Favours_, which are the main substance of Seneca's writings.