Debates about the demise of the Roman city have often considered the spread of Christianity as a factor in destroying the classical concepts that underwrote it. One way of understanding the impact of Christianity on classical urbanism is to examine its influence on concepts of the first city. By identifying the elements that make up a city, these ideas offer a useful means of investigating how writers perceived the fundamental nature of the city. Genesis clearly attributes the first city to Cain, something potentially in conflict with classical narratives of the city as part of a civilizing process. In practice, while Cain’s city was to become dominant in the early middle ages, it had little impact on late antique Christian thought prior to the late fourth century and particularly Augustine’s popularization of it in De civitate Dei. Earlier Christian writers such as Lactantius and Eusebius instead engaged with classical first cities in a wide variety of ways reflective of the debates in which they participated. Lactantius rejected these models of urbanism because they contradicted his understanding of history, morality, and justice, whereas Eusebius embraced them as a way of considering the role of the divine in human development. The differences in their approaches point to the variety in early Christian approaches to the city, suggesting that the city of God was not necessarily inherently incompatible with the classical city.