Recent surveys of Russia's emergence as an empire have asserted that Russians recognized no clear-cut boundaries between the Rus' metropole and the other territories affiliated with Rossiia, the empire. But was this in fact true? The evolution of Russia's southern boundaries in the seventeenth century is a story of exclusion rather than integration. Before the Russian state would attempt to annex the Don region, it first enacted, then enforced, a high degree of separation between itself and the Don. The sum of various seventeenth-century measures contributed to a demarcated and patrolled cordon sanitaire between Russia's underprivileged ethnic core and privileged Cossack frontier.

This chapter will argue that an imperial boundary – a system of earthen and wooden fortifications called the Belgorod line – made a transformative impact on both Russia and the Don region. The Muscovite state moved from a system of open frontiers to a patrolled infrastructure that demarcated the limits of Rus' and gave tangible expression to territorial sovereignty. It also inadvertently inaugurated a new era in the settlement history of the Don region: long-distance migration by isolated individuals or small groups gave way to inter-regional migration on a much wider scale. In order to assert and empirically enforce its sovereignty claims in the south, the state began to utilize its new boundary infrastructure not simply to prevent Tatar raids, but also to regulate the migration of its serfs and subjects into territories beyond its jurisdiction in the Don steppe frontier.