The early Christian philosophy of Augustine of Hippo was heavily influenced by Plato. A key change brought about by Christian thought was the moderatation of the Stoicism and theory of justice of the Roman world, as well emphasis on the role of the state in applying mercy as a moral example. Augustine also preached that one was not a member of his or her city, but was either a citizen of the City of God (Civitas Dei) or the City of Man (Civitas Terrena). Augustine's City of God is an influential work of this period that attacked the thesis, held by many Christian Romans, that the Christian view could be realized on Earth.
What does Civitas Dei mean?
City of God