Diocletian also restructured the Roman government by establishing the Tetrarchy, a system of rule in which four men shared rule over the massive Roman Empire. The empire was effectively divided in two, with an Augustus and a subordinate Caesar in each half.
Of all the factors draining the empire of its ability to survive, four stand out: the changing nature of the external threat to the empire's western borders; the frequent civil wars among claimants to the imperial throne; the migration and settlement of large, armed and culturally hostile barbarian populations within ...
