This paper uses the natural experiment of Argentina’s integration into world markets in the late-nineteenth century to provide evidence on the role of internal geography in shaping the effects of external integration. We develop a quantitative model of the distribution of economic activity across regions and sectors. The model predicts a spatial Balassa-Samuelson effect, in which locations with better access to world markets have higher population densities, higher shares of employment in the non-traded sector, higher relative prices of non-traded goods, and higher land prices relative to wages. We use the model and data on population density and sectoral employment shares to recover sufficient statistics that isolate the economic mechanism...