Cities of the Gods is a historical study of the theory of Utopian communism in ancient Greek thought, identifying and assessing its several currents. The author looks at the reason for the decline of the Utopian traditions after c. 150 BC and suggests that the main factor was the Roman conquest of the Greek world, which produced a more conservative intellectual climate. He concludes by looking at the evidence for the survival of utopian traditions, particularly their influence on early Christianity.