Complex sentence: The Army of the Rhine was deployed along a frontline some 70 kilometres in length and was opposed by an Allied army of around 70,000 Prussians, Austrians and Saxons under Prussian Field Marshal von Möllendorf held strong defensive positions and elevated terrain.
Split into simpler sentences: The Army of the Rhine was deployed along a frontline some 70 kilometres in length. It was opposed by an Allied army of around 70,000 Prussians, Austrians and Saxons under Prussian Field Marshal von Möllendorf which held strong defensive positions and elevated terrain.