During much of the nineteenth century, Rio de Janeiro, the Brazilian capital, was under a selective curfew that made it a crime to be in the city's public spaces after dark. The curfew bent normal rules and attenuated supposedly universal rights, overtly discriminating between people on the basis of class and race. Rules that legally defined the nighttime did not come from any national statute, or from newly independent Brazil's liberal Constitution (1824) or its Criminal Code (1830). Instead, Rio's nocturnal sociolegal world was the product of police edicts, on-the-ground policing practice, and city ordinances. It also emerged from the actions of people who used the darker hours for work, play, and resistance against oppression, especially members of the city's immense enslaved population and the growing number of free persons of African descent. In other words, this is a phenomenon of urban governance that allows, and indeed forces us to look beyond the nineteenth-century nation-state to understand the exercise of power at a local level. This article explores how the curfew established patterns and means of limiting the basic freedom to move about the city. It was at night when both the necessity and fragility of what jurists in Brazil called the “freedom to come and go” came into view. The daily transition between day and night enacted juridical changes that, although invisible at the national level, fundamentally shaped the social categories that determined people's places in society in ways that historical research has yet to explore.