This monograph attempts in a systematic way the interpretation of Caracalla's measure (Constitutio Antoniniana, 212 A.D.) to extend the Roman citizenship practically to all free inhabitants of the Roman empire. To attain this, various sources are adduced and thoroughly examined, as on the ruling concepts of the Severan dynasty, the contemporaneous importance of Alexander's image, the religious and some egalitarian traits of the period. There follows a detailed examination of the consequences of the same edict, which shows that not only numerically (great numbers of new Roman citizens) but also on the levels of social, legal, financial and political—psychological development of the empire the Constitutio Antoniniana was much more important that the earlier scholarship was usually ready to accept.