Neither could his march, when begun, be directed with certainty on Wavre. The first traces of the Prussians which he could receive, seemed to intimate, on the contrary, that they were retiring towards Namur, which induced Grouchy to push the pursuit in the latter direction, and occasioned the loss of some hours. From all these concurring reasons, the maréchal shows distinctly, that he could not have attained Wavre on the evening of the 17th June, because he had no orders to go there till noon, nor troops ready to march till three o'clock; nor had either Napoleon or his general any foreknowledge of the motions of Blucher, which might induce them to believe Wavre was the true point of his retreat. It was not till he found the English resolved to make a stand at Waterloo, and the Prussians determined to communicate with them, that Napoleon became aware of the plan arranged betwixt Wellington and Blucher, to concentrate the Prussian and English armies at Waterloo. This was the enigma on which his fate depended, and he failed to solve it. But it was more agreeable, and much more convenient, for Napoleon to blame Grouchy, than to acknowledge that he himself had been surprised by the circumstances in which he unexpectedly found himself on the 18th.
Meantime, having detached Grouchy to pursue the Prussians, Napoleon himself moved laterally towards Frasnes, and there united himself with the body commanded by Maréchal Ney. His purpose was to attack the Duke of Wellington, whom he expected still to find in the position of Quatre-bras.
But about seven in the morning, the duke, having received intelligence of the Prince Maréchal Blucher's retreat to Wavre, commenced a retreat on his part towards Waterloo, in order to recover his communication with the Prussians, and resume the execution of the plan of co-operation, which had been in some degree disconcerted by the sudden irruption of the French, and the loss of the battle of Ligny by the Prussians. The retreat was conducted with the greatest regularity, though it was as usual unpleasant to the feelings of the soldier. The news of the battle of Ligny spread through the ranks, and even the most sanguine did not venture to hope that the Prussians would be soon able to renew the engagement. The weather was dreadful, as the rain fell in torrents; but this so far favoured the British, by rendering the ploughed fields impracticable for horse, so that their march was covered from the attacks of the French cavalry on the flanks, and the operations of those by whom they were pursued were confined to the causeway.