September 6-22, 1937 - In the Asturias region of northern Spain, Nationalist troops attack the Republican defenses in El Mazuco Pass, beginning the Battle of El Mazuco. Lasting 16 days, the battle saw 5,000 Republican soldiers, with no air or artillery support, valiantly defend the pass against 33,000 Nationalists. Resisting against near-constant artillery and aerial bombardment, the Republicans exacted a heavy toll from the Nationalists, while slowly being forced to give ground. By September 16, they had been pushed back to the top of the pass, which they defended for six days before being overrun. The Battle of El Mazuco was one of the last battles of the Spanish Civil War fought in the northern part of the country.