The French army crossed the border into the southern Netherlands, now Belgium, on 15 June, Napoleon skilfully inserting his army between the allied armies of Wellington and von Blücher. With the Anglo-allied on his left and the Prussians on his right, he then despatched Marshal Ney to advance on Wellington at Quatre-Bras, which he did cautiously, allowing time for Wellington to reinforce his outnumbered lines. Meanwhile the Prussians were located on sloping ground to the north of Ligny. The Prussians had deployed three corps, mostly on forward slopes, where they were exposed to accurate French artillery fire. Napoleon’s plan called for Marshal D’Erlon, attached to Ney’s command, to march eastward and attack the Prussian left, but due to conflicting orders he spent the day marching his men between the battlefields. The Prussians, despite serious losses, held on and just as D’Erlon was due to finally arrive enemy troops were reported south of Napoleon’s positions. As the French turned to face this apparent threat Blücher launched a major attack, which was repulsed. The mysterious enemy turned out to be the missing D’Erlon’s corps. The French advanced through Ligny, followed by cavalry in support; despite desperate fighting the Prussians eventually gave ground, retreated in reasonable order northwards and were able to maintain contact with Wellington. Meanwhile, on the following morning, Napoleon had detached Grouchy’s corps to pursue the retreating Prussians.
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