This papers gives new evidence on the relationship between integration (internal and external)and industrial agglomeration in the presence of scale economies by testing directly one of the predictions that can be derived from Krugman (1991).That is,the existence of regional nominal wage gradients and its transformation following the changes in trade regimes.In this framework,we analyze whether or not,during the period 1856-1995,protectionists policies could have favored the loss of centrality of the main coastal location of Spanish industry (Barcelona).