The recognition (which we see already in Homer) that a limitation was put upon human affairs is one of the greatest and most fundamental discoveries of Greek political thought and was to have a glorious posterity in Western political history in general. Republican Rome was no different, and, upon Octavian’s accession to the imperium, things did not change fundamentally. Even the emperors admitted that there was a limit to Roman expansion–the Hadrian wall is a telling example.
We are, however, faced with a problem after the crisis of the 3rd century and the rise of Diocletian. This era is often called by modern historians the Dominate, after Diocletian’s self-bestowed title of Dominus, “master.” Many have seen in the emperor taking on the title of dominus a new conception of state authority, a conception that was essentially more authoritarian in form, and where those who were up until then citizens became subjects. The dominus was, in Roman Republican tradition, the equivalent of the Greek tyrannos, tyrant, and meant master or owner (of a slave for example). That the emperor took on this title, and was called therewith, is a significant step away from the Republican tradition, and, at first, from a certain conception of freedom, yet we should not exaggerate the implications of this. Late Antiquity was certainly an era of violence: torture was in common use, but this should not be blamed upon Diocletian or any single person. It was rather the expression of something deeper that was running through society, the visible face of a more profound social crisis that ran through all levels of society. The title of dominus was in many ways an adaptation and a solution to these tensions.