The new Stoicism characterized the Roman Empire philosophically. The doctrine of universal brotherhood of the third Stoa finds numerous points of contact with Christianity. The work of Lucio Annaeus Seneca, a contemporary of the redemptive pilgrimage of Jesus of Nazareth, is an example of this connection between Stoicism and Christianity. The deep religious pathos that pervades Seneca’s work has led him to be described, by some authors, as a follower of Christianity. It is in Roman Stoicism that we find the first precise formulation of natural law, which we can locate within humanistic natural law. Among the versions of iusnaturalism in history, it is the humanistic natural law that has achieved the greatest historical fecundity, for its permanent struggle for the defense of human dignity and for having fulfilled the important mission of educating humanity to build a civilized coexistence. In this connection between Stoicism and Christianity, the germ of the paradigm of justice, or material validity, typical of the Constitutional State of Law can be found.