How d’Erlon had arrived in this position may be explained with little difficulty. When Napoleon’s aide-de-camp, Laurent, reached Gosselies with the morning order, he found that the First Corps was already marching towards Quatre-Bras, and that d’Erlon himself had gone forward to Frasnes. Laurent hastened to find him, and on overtaking the columns of the First Corps on his way, he took upon himself the responsibility of changing their direction towards St Amand. D’Erlon, on learning what had been done, rode off at once to join his Corps, sending word to Ney to inform him what had happened. The road from Frasnes towards St Amand lay through Villers-Perruin, and it was this direction which brought the column into such an unexpected position towards the French rear. On reaching Villers-Perruin, however, d’Erlon sent out a Light Cavalry Brigade to his left, as a precautionary measure. This Brigade encountered a Prussian Brigade of Hussars and Lancers under Marwitz, who withdrew slowly and in good order. Girard’s Division, perceiving the Prussians retire, became reassured, and moved forward to its original position. But now, d’Erlon received from Ney a most urgent and peremptory order to rejoin him at once. D’Erlon, who acted under Ney’s immediate orders, decided that it was his duty to obey those orders; and since he had received no definite instructions from the Emperor as to how he should act when he had brought his Corps on the field, he turned about and left the ground. Thus he was too late in his return to be of use to Ney at Quatre-Bras, and the eccentric direction given to his columns, although the natural outcome of his previous dispositions, served to postpone Napoleon’s great attack with his Guard for two hours; and, when the addition of 20,000 men might have entirely overwhelmed the Prussians, he calmly withdrew his men.
D’Erlon’s error was his inaction when he arrived on the field, and not so much his diversion from Ney’s orders. He must have known that he could not return to Quatre-Bras in time to be of any service; but that by following up Marwitz, and falling on the rear of the Prussian right wing, he would be most likely to render the very greatest assistance to Napoleon. How he could have failed to realise the importance of his presence at such a juncture surpasses all imagination. The very fact that Marwitz’s Brigade had been able to present some show of compactness before Jacquinot’s Cavalry might have proved to him that there was still a stout resistance to be expected on the part of the Prussians. Again, we think Napoleon should have sent instructions as to how d’Erlon should act, by his aide-de-camp, in the event of the strange column being French. Had d’Erlon remained on the left wing to assist Ney, Quatre-Bras might have been won by the French. Had he realised the uselessness of a return march to Ney when he was yet at hand to help Napoleon, and thrown all his weight into the struggle at Ligny, he would have been of the greatest use in overwhelming the Prussians.