Why does contentious political challenge start in central public squares then move to residential neighborhoods in different parts of the city? Does the built environment play a role in facilitating (or inhibiting) challenge, or channeling it towards (or away from) violence? A role for the built environment in challenge and conflict has been established in urban studies and sociology, but it has been largely neglected in political science. Moreover, the modalities by which physical space structures conflict remain underexplored. This paper unpacks these mechanisms, focusing on two-time scales: (1) in the long run, some built environments facilitate the reproduction of social networks through patterns of migration, and (2) in the short run, built environments shape perceptions of efficacy among protesters/combatants regarding the prospect of social networks to sustain contention and protect challengers. In this sense, residents of some neighborhoods participate in high risk activism not simply to defend people in their social circles but also their physical living spaces. We test these hypotheses empirically by examining variation in patterns of violence in neighborhoods with varying spatial layouts in Damascus and Homs during the early months of the Syrian uprising of 2011. We employ a mixed-methods approach. First, we quantitatively evaluate the determinants of violence with a range of fine-grained data, including a novel measure of the built environment (using the Space Syntax analysis technique developed at the UCL Bartlett Faculty of the Built Environment) and original data on protest events, violence, and the location of security agency bases. We complement this analysis with qualitative evidence gathered in interviews with members of the social networks under examination and a detailed reading of local press sources and social media. Ultimately, the paper reconceptualizes the power of the built environment and introduces new indicators to capture the various ways in which it can channel the progression of violence in the city.