Are transaction costs and half-lives between two cities the same in both directions in traditional city-based monetary systems? Market conditions and political circumstances may not justify this assumption; and we provide evidence that it does not hold in the 1825-1885 period in Spain.Moreover, we show empirical evidence that market integration in Spain from 1875 to 1885 was a slow process of monetary unification with decreasing transaction costs, and a very inefficient convergence. Therefore, full integration did not happen in the period 1875-1885 and had to wait until mid-1880s, when the Spanish money-market was unified due to financial innovations.