This paper documents a rare phenomenon: the consequence of the dominance of a single criminal gang in the city of São Paulo, the Primeiro Comando da Capital (PCC). Using unique data to identify entry in geographically well-delimited areas – the Favelas - we explore the timing of the expansion of geographical dominance to estimate the causal impact of its dominance on property and violent crime. Pax Monopolista caused a reduction in violent crime but no impact on property crime.