Complex sentence: Grouchy continued the march on Wavre and engaged the Prussians by launching a series of heavy attacks against Thielmann's rearguard, although out-numbered the Prussians held their ground.
Split into simpler sentences: Grouchy continued the march on Wavre and engaged the Prussians by launching a series of heavy attacks against Thielmann's rearguard. Although out-numbered the Prussians held their ground.