How does gaining an empire change the conqueror? Why is the assimilation of new populations, goods, and ideas sometimes seen as a marker of a people's greatness, and at other times as a dangerous threat from within? This project analyzes immigration to three capital cities: Athens (5th-4 th centuries BCE), Rome (1st-4th centuries CE), and Chang'an, capital of Tang dynasty China (7th-10 th centuries CE). It analyzes ancient textual and archaeological evidence through the lens of borderland theory to argue that the boundaries surrounding immigrant neighborhoods transformed each of these iconic cities into urban borderlands where ideas of social otherness had physical analogues. It was in these urban borderlands that the problem of how to accommodate new populations into existing structures of imperial domination was worked out.

In their respective heydays, Athens, Rome, and Chang'an functioned as centers of government, economic powerhouses, global schools, sites of religious pilgrimage, and tourist attractions. Many of the diverse immigrants they attracted settled in the neighborhoods at the center of this analysis: Athens' port of Piraeus, Rome's Trans Tiberim district, and Northwest Chang'an. These communities stood out as "small worlds" within their cities at large, where ethnic, linguistic, and cultural differences overlapped with physical boundaries such as rivers, roads, and walls. Residents carved out places for themselves in their new homes by learning how to skillfully navigate these boundaries. Whether by traversing the urban landscape during their daily commute, participating in civic or religious ceremonies, or attending festivals and entertainments, newcomers came into contact with locals on a daily basis. These interactions blurred lines between "us" and "them" in ways that called into question the limits of national identity and, depending on the circumstances, could either fan the flames of xenophobia or nurture new cultural syntheses. In this sense, life at the center of the Athenian, Roman, and Tang empires resembled that on their outer frontiers, where "civilized" insiders and "barbarian" outsiders lived poised between intimate coexistence and violent rejection. Assessing these imperial capitals as urban borderlands allows us see that this tension was not an aberration or strictly a regional phenomenon. It was quite literally built into the heart of all three empires.