But while Roman society persisted in a state of peaceful security, it already contained within itself the seeds of dissolution.  The long peace and uniform government of the Romans introduced a slow and secret poison into the vitals of the empire.  The minds of men were gradually reduced to the same level, the fire of genius was extinguished, and even the military spirit evaporated.  The citizens received laws and covenants from the will of their sovereign, and trusted for their defence to a mercenary army.  Of their ancient freedom nothing remained except the name, and that Augustus, sensible that mankind is governed by names, was careful to preserve.

It was by the will of the senate the emperor ruled.  It was from the senate that he received the ancient titles of the republic—­of consul, tribune, pontiff, and censor.  Even his title of imperator was decreed him, according to the custom of the republic, only for a period of ten years.  But this specious pretence, which was preserved until the last days of the empire, did not mask the real autocratic authority of the emperor.  The fact that he nominated citizens to the senate was proof, if proof were needed, that the independence of that body was destroyed; for the principles of a free constitution are irrecoverably lost when the legislative power is nominated by the executive.

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.