The Battle of the Ebro (Spanish: Batalla del Ebro, Catalan: Batalla de l'Ebre) was the longest and bloodiest battle of the Spanish Civil War. It took place between July and November 1938, with fighting mainly concentrated in two areas on the lower course of the Ebro River, the Terra Alta comarca of Catalonia, and the Auts area close to Fayón (Faió) in the lower Matarranya, Eastern Lower Aragon. These sparsely-populated areas saw the largest array of armies in the Civil War. The results of the battle were disastrous for the Second Spanish Republic with tens of thousands of dead and wounded, with little effect on the relentless advance of the Nationalists.
http://en.wikipedia.org/wiki/Battle_of_the_Ebro 
Memorials 
