ABSTRACT: This paper discusses the “metropolitan miracle” that has taken place in Colombia since the early 1990s and which consists of the radical improvement of security in two of Colombia’s three major cities (Bogotá and Medellín) - an improvement that experts considered highly unlikely. This phenomenon has been described, but not explained, and this is the purpose of our paper: to provide a political explanation of the miracle. We suggest here that the explanation lies in politics: coalitions, organisation, and state building. We claim that: a) the metropolitan miracle happened because a new, heterogeneous, governing coalition came to power which had strong enough incentives to disentangle itself from the dynamics of private provision of security; and b) the miracle was more likely to occur in very large cities. In contrast to Europe, where relatively small size can coexist with prosperity, for example via conurbations, in Latin America in general - and in Colombia in particular - only in the metropolis does the middle class have substantial power.