The Douro is the largest river of the Iberian Peninsula by discharge. It rises at the Pico de Urbión, the highest summit of the Picos de Urbión, first flows through Duruelo de la Sierra in the Spanish province of Soria, meanders briefly south, then flows generally west through the northern part of the Meseta Central in Castile and León into northern Portugal. Its largest tributary is the right-bank Esla. The Douro flows into the Atlantic Ocean at Porto, the second largest city of Portugal.