The Republican defence of El Mazucu 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.

The leader of the Nationalist forces surrounding Asturias, General Fidel Dávila, attacked from the south and from the east, expecting little resistance from the demoralized Republicans.

However, the routes the Nationalists then had to take were commanded by the limestone walls of the Sierra de Cuera on the north of the front and the Deva Gorge to the south.

The Nationalists had to clear the defenders from these mountains in order to advance, and to do that they planned a pincer movement moving southwest from Llanes and west, along Cares river, from Panes towards Cabrales.

In response to these setbacks, the German Condor Legion was called in and for the first time carpet-bombed a military target, the Republican forces defending the approach to El Mazucu.

On 7 September further attacks were halted and the fronts stabilized; a noted Republican commander, Higinio Carrocera, arrived, with three battalions and 24 heavy machine guns.

The fog having returned on 10 September, an all-out attack by the I Brigade took the hill of Biforco (below the pass of El Mazucu), but this was still dominated by the heights of Llabres, from where the Republicans hammered the area with machine guns and rolled down carbide drums filled with explosive.

The better weather on 18 September at noon brought three waves of airborne strafing from 'strings' of Junkers and Fiat fighters, and possibly Heinkel 51s based on the Cue Aerodrome[citation needed].

The defence of El Mazucu also allowed the Republicans further west in Asturias a certain breathing space and a chance to regroup, but ultimately this made little difference.