Map of The Battle of Ligny, preceding Waterloo by two days.  The Prussians were forced to retreat. Field Marshal Blucher, the commander of the Prussian army, retreated towards Wavre, so as to be headed towards Waterloo, thus helping Wellington.  As it turned out, it was a decisive move, as he was able to not only occupy 33,000 pursuing French, but also fall upon the French right flank at Waterloo.
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