According to Plato

According to Plato, an ideal polis is a state which is based on fairness and virtue. The ideal state is a type of social and political organization that permits individuals to make the most of their potentials, serve their fellow citizens, and live in harmony with universal laws and truths. Augustine is of the view that men can only do good if they follow the will of God. He wants people to realize that His order is superior. In short Plato has based his theory on individual and Augustine has based his theory on God only.
As I comprehend, Augustine believed that an ideal city is to be based on the laws of God. So in order to make Plato’s ideal polis to resemble the city of God, Augustine would make it necessary to abide by the rules provided by the Divine. Plato’s ideal polis is ruled by the philosophers or the kings and these people must be fully educated, be able to understand the difference between the visible and the invisible world. Augustine would have made compulsory for the ruling class to get complete knowledge of the religion as well so as to govern the state according to the rules set by the God. Similarly, Augustine would have promoted feelings of love among the individuals, as according to Augustine, love of God gets mostly expressed through loving one’s neighbor.