Moreover, the dependence of the emperor on the legions completely subverted the civil authority. To keep the military power, which had given him his position, from undermining it, Augustus had summoned to his aid whatever remained in the fierce minds of his soldiers of Roman prejudices, and interposing the majesty of the senate between the emperor and the army, boldly claimed their allegiance as the first magistrate of the republic. During a period of 220 years, the dangers inherent to a military government were in a great measure suspended by this artful system. The soldiers were seldom roused to that fatal sense of their own strength and of the weakness of the civil authority which afterwards was productive of such terrible calamities. The emperors Caligula and Domitian were assassinated in their palace by their own domestics. The Roman world, it is true, was shaken by the events that followed the death of Nero, when, in the space of eighteen months, four princes perished by the sword. But, excepting this violent eruption of military licence, the two centuries from Augustus to Commodus passed away unstained with civil blood and undisturbed by revolution. The Roman citizens might groan under the tyranny, from which they could not hope to escape, of the unrelenting Tiberius, the furious Caligula, the profligate and cruel Nero, the beastly Vitellius, and the timid, inhuman Domitian; but order was maintained, and it was not until Commodus, the son of Marcus Aurelius Antoninus, the philosopher, succeeded to the authority that his father had exercised for the benefit of the Roman Empire that the army fully realised, and did not fail to exercise, the power it had always possessed. During the first three years of his reign the vices of Commodus affected the emperor rather than the state. While the young prince revelled in licentious pleasures, the management of affairs remained in the hands of his father's faithful councillors; but, in the year 183, the attempt of his sister Lucilla to assassinate him produced fatal results. The assassin, in attempting the deed, exclaimed, "The senate sends you this!" and though the blow never reached the body of the emperor, the words sank deep into his heart. He turned upon the senate with relentless cruelty. The possession of either wealth or virtue excited the tyrant's fury. Suspicion was equivalent to proof; trial to condemnation, and the noblest blood of the senate was poured out like water.