The mystery as to the movements of D’Erlon and his 20,000 men has never been fully cleared up.  The evidence collected by Houssaye leaves little doubt that, as soon as the Emperor realized the serious nature of the conflict at Ligny, he sent orders to D’Erlon, whose vanguard was then near Frasnes, to diverge and attack Bluecher’s exposed flank.  That is to say, D’Erlon was now called on to deal the decisive blow which had before been assigned to Ney, who was now warned, though very tardily, not to rely on the help of D’Erlon’s corps.  Misunderstanding his order, D’Erlon made for Fleurus, and thus alarmed Napoleon and delayed his final blow for wellnigh two hours.  Moreover, at 6 p.m., when D’Erlon might have assailed Bluecher’s right with crushing effect, he received an urgent command from Ney to return.  Assuredly he should not have hesitated now that St. Amand was almost within cannon-shot, while Quatre Bras could scarcely be reached before nightfall; but he was under Ney’s command; and, taking a rather pedantic view of the situation, he obeyed his immediate superior.  Lastly, no one has explained why the Emperor, as soon as he knew the errant corps to be that of D’Erlon, did not recall him at once, bidding him fall on the exposed wing of the Prussians.  Doubtless he assumed that D’Erlon would now fulfil his instructions and march against Bry; but he gave no order to this effect, and the unlucky corps vanished.

At that time a desperate conflict was drawing to a close at Quatre Bras.  Ney had delayed his attack until 2 p.m.; for, firstly, Reille’s corps alone was at hand—­D’Erlon’s rearguard early on that morning being still near Thuin—­and, secondly, the Marshal heard at 10 a.m. that Prussian columns were marching westwards from Sombref, a move that would endanger his rear behind Frasnes.  Furthermore, the approach to Quatre Bras was flanked by the extensive Bossu Wood, and by a spinney to the right of the highway.  Reille therefore counselled caution, lest the affair should prove to be “a Spanish battle where the English show themselves only when it is time.”  When, however, Reille’s corps pushed home the attack, the weakness of the defence was speedily revealed.  After a stout stand, the 7,000 Dutch-Belgians under the Prince of Orange were driven from the farm of Gemioncourt, which formed the key of the position, and many of them fled from the field.

But at this crisis the Iron Duke himself rode up; and the arrival of a Dutch-Belgian brigade and of Picton’s division of British infantry, about 3 p.m., sufficed to snatch victory from the Marshal’s grasp.[493] He now opened a destructive artillery fire on our front, to which the weak Dutch-Belgian batteries could but feebly reply.  Nothing, however, could daunt the hardihood of Picton’s men.  Shaking off the fatigue of a twelve hours’ march from Brussels under a burning sun, they steadily moved down through the tall crops of rye towards the farm and beat off a fierce attack of Pire’s horsemen.