Since the antique axial age, religion and law have been interconnected by the ideas of unity and truth. Not only Jews and Christians, but also Greek philosophers, such as Parmenides, assumed that there were not many, but rather only one true God; similarly, the many different laws of the antique states and communities were complemented by the idea of a law common to all peoples (ius gentium) or of some kind of natural law (ius naturae). Since medieval times both ideas have gained momentum. The people of Europe were connected not only as members of the Roman Church, but also by the roman-canon ius commune; and in early modern natural law religious and legal truth were closely intertwined. Since the reformation, however, the idea of legal unity seems to have gained importance as religious truth and unity assumed a utopian character as a result of the confessional divide of Christianity. The ideas of a reasonable legal order common to all human beings underlies both, the secular systems of a law of reason and the enlightenment’s codification movement. Of course, natural-law ideas lost their appeal during the 19th and 20th centuries; yet meanwhile, basic universal standards of justice have become positive law in modern constitutions; thus a non-positive natural could appear obsolete. Nonetheless, the idea of universal human rights made it possible for modern constitutional courts to formulate a new common law of (pre-state?) human rights.