Such was stoicism, of which Marcus Aurelius was and still remains the foremost expression. He admitted that as emperor his first duty was to sacrifice himself for the public and he did his duty with a constancy which ultimately cost him his life. Among these duties was the great duty of naming his successor. The Roman Empire never became strictly hereditary. It hinged, as perhaps no other equally developed system ever hinged, upon the personality of the emperor, who incarnated the administrative bureaucracy which gave effect to the _Pax Romana_ and the _Romana lex_ from the Euphrates to the Atlantic and from Scotland to the Tropic of Cancer. Of all men Marcus Aurelius was the most conscientious and the most sincere, and he understood, as perhaps no other man in like position ever understood, the responsibility which impinged on him, to allow no private prevention to impose an unfit emperor upon the empire But Marcus had a son Commodus, who was nineteen when his father died, and who had already developed traits which caused foreboding. Nevertheless, Marcus associated Commodus with himself in the empire when Commodus was fourteen and Commodus attained to absolute power when Marcus died. Subsequently, Commodus became the epitome of all that was basest and worst in a ruler. He was murdered by the treachery of Marcia, his favorite concubine, and the Senate decreed that “his body should be dragged with a hook into the stripping room of the gladiators, to satiate the public fury.” [Footnote: _Decline and Fall_, chap. iv.] From that day Rome entered upon the acute stage of her decline, and she did so very largely because Marcus Aurelius, the ideal stoic, was incapable of violating the great law of nature which impelled him to follow not reason, but the path of least resistance in choosing a successor; or, in other words, the instinct of heredity. Moreover, this instinct and not reason is or has been, among the strongest which operate upon men, and makes them automata. It is the basis upon which the family rests, and the family is the essence of social cohesion. Also the hereditary instinct has been the prime motor which has created constructive municipal jurisprudence and which has evolved religion.