Complex sentence: German infantry reinforcements of the 6th Army arrived in the area during October and began attacks from Arras north to Armentières in late October, which were faced by III Corps from Rouges Bancs, past Armentières north to the Douve river, beyond the Lys.
Split into simpler sentences: German infantry reinforcements of the 6th Army arrived in the area during October. The 6th Army began attacks from Arras north to Armentières in late October, which were faced by III Corps from Rouges Bancs, past Armentières north to the Douve river, beyond the Lys.