 None of these small, fast-flowing rivers is navigable.Major Spanish riverside towns include Soria, Almazán, Aranda de Duero, Tordesillas, Zamora and major Portuguese towns include Miranda do Douro, Foz Côa, Peso da Régua, Lamego, Vila Nova de Gaia, and Porto.The most populous cities along the Douro River are Valladolid and Zamora in Spain, and Porto and Vila Nova de Gaia in Portugal.