Citizenship is one of the most debated issues in the present-day Europe, and therefore we wish to open up contextualized discussions on its roots in the Greco-Roman Antiquity. Citizenship and its criteria were redefined many times during the Roman rule in the Mediterranean area. In the conquests and crises, new ideas of defining the good members of Roman society emerged. The Constitutio Antoniniana by Emperor Caracalla in 212 granted citizenship to all free provincials. Philosophers and orators cherished the idea of cosmopolitan citizenship. Recognition of loyal Roman citizens/subjects in terms of religion became more emphatic from the early 3 rd century CE onwards and this continued in the course of the Christianization of the Empire.