We estimate the contribution of spatial centrality to determine city size. We do this using archaeological data on cities of the region of Bukhara observed in the 9th CE. The unique feature of this region is that it was homogeneous in all respects. Homogeneity rules out confounding factors and endogeneity issues. We estimate a simple general equilibrium spatial model. The estimated model predicts almost perfectly the 9th century city size thus showing that spatial centrality is the major determinant of city size. The Silk Road contributes to explaining what centrality cannot. Interestingly, the model estimated for the 9th century explains about 20% of the variation in population shares for the US commuting zones.  Lastly, we estimate that infrastructures in the US have contributed to an 8% increase in welfare.