The Battle of El Mazuco was fought between 6 and 22 September 1937, between the Republican and Nationalist armies during the Spanish Civil War as a part of the War in the North campaign. The Republican defence of El Mazuco and the surrounding mountains halted the Nationalist advance into eastern Asturias, despite their forces being outnumbered sevenfold. After weeks of intense fighting over extreme terrain the defenders were eventually overwhelmed, and the Nationalists were then able to link up with their forces advancing from León, leading to the fall of Gijón and the abandonment of Asturias, the last Republican province in North-West Spain.