Empire, down to the time of Diocletian, beheld a constant mutation of rulers, sometimes benevolent, or at least comparatively good, whose reigns however were often but of short duration, sometimes weak and spiritless, and sometimes again tyrants of the most abject and atrocious cast. Among these latter Sovereigns, however, who in cruelty and arbitrary caprice, resembled the first successors of Augustus, there were no characters possessed of that strong Roman sense which distinguished Tiberius; and the empire in their hands assumed daily more and more a thoroughly effeminate and oriental complexion. Nothing was more subject to chance than the right of succession in the Roman empire, where the arbitrary application of the Roman principle of adoption opened a wide field to the contention of parties; without including the frequent recurrence of conspiraces in a military empire, which, as it was formed by a military conspiracy, ever retained the stamp of its origin. Augustus had employed his whole life, not without apparent success, for a time at least, in endeavouring to give to authority, acquired by force of arms, the colour and forms of legitimacy. But how could it be ever forgotten that he, as well as Cæsar, had been raised to the Imperial throne by the army, and amid the struggles of factions, conspiracies, and civil wars. The soldiers knew this, and recollected but too well the source whence the supreme power in the state had emanated. The influence of the Prætorians, especially, was, from their origin, very considerable, as they surrounded the Emperor, and formed his body-guard. By virtue of his office the leader of the Prætorians had a sort of negative and controlling power, like that of the Censor and popular Tribune in the ancient republic, except that this functionary wielded the sword,--a power in some degree acknowledged by the Emperor himself, as it was accounted one of the highest merits of Trajan, that to the chief of that troop which defended the person, and often decided the fate, of the Emperor, he delivered the sword with these words: "For me, if I govern well--against me, if I should become a tyrant."