During a long period of two hundred and twenty years from the establishment of this artful system to the death of Commodus, the dangers inherent to a military government were, in a great measure, suspended. The soldiers were seldom roused to that fatal sense of their own strength, and of the weakness of the civil authority, which was, before and afterwards, productive of such dreadful calamities. Caligula and Domitian were assassinated in their palace by their own domestics: * the convulsions which agitated Rome on the death of the former, were confined to the walls of the city. But Nero involved the whole empire in his ruin. In the space of eighteen months, four princes perished by the sword; and the Roman world was shaken by the fury of the contending armies. Excepting only this short, though violent eruption of military license, the two centuries from Augustus to Commodus passed away unstained with civil blood, and undisturbed by revolutions. The emperor was elected by the _authority of the senate, and the consent of the soldiers_. The legions respected their oath of fidelity; and it requires a minute inspection of the Roman annals to discover three inconsiderable rebellions, which were all suppressed in a few months, and without even the hazard of a battle. In elective monarchies, the vacancy of the throne is a moment big with danger and mischief. The Roman emperors, desirous to spare the legions that interval of suspense, and the temptation of an irregular choice, invested their designed successor with so large a share of present power, as should enable him, after their decease, to assume the remainder, without suffering the empire to perceive the change of masters. Thus Augustus, after all his fairer prospects had been snatched from him by untimely deaths, rested his last hopes on Tiberius, obtained for his adopted son the censorial and tribunitian powers, and dictated a law, by which the future prince was invested with an authority equal to his own, over the provinces and the armies. Thus Vespasian subdued the generous mind of his eldest son. Titus was adored by the eastern legions, which, under his command, had recently achieved the conquest of Judæa. His power was dreaded, and, as his virtues were clouded by the intemperance of youth, his designs were suspected. Instead of listening to such unworthy suspicions, the prudent monarch associated Titus to the full powers of the Imperial dignity; and the grateful son ever approved himself the humble and faithful minister of so indulgent a father.