monarchy was adoptive: the emperor transmitted his authority not to his offspring but to the ablest man he could find; he adopted this man as his son, trained him in the functions of government, and gradually surrendered to him the reins of power. The system worked well, partly because neither Trajan nor Hadrian had a son, and the sons of Antoninus Pius died in childhood. Marcus Aurelius had a son, Commodus, who succeeded him because the philosopher failed to name another heir; soon chaos was king.
