6. It may be thought by some that the effect upon the corps of Bülow and Pirch I. of the appearance of Marshal Grouchy’s command, marching from Moustier and Ottignies upon Lasne and St. Lambert, has been stated too strongly in the text. But we cannot think so. Imagine 30,000 or 40,000 men marching in a long column along miry roads to attack an enemy, and still some miles from the field of battle, perceiving a body of troops of apparently equal or nearly equal strength moving right upon their line of march, which is also their line of communications. How many officers in Bülow’s position would not have halted to resist such an attack? It is to be observed, that the dilemma in which Bülow and Pirch I. were placed by knowing that Grouchy was attacking Wavre was quite a different one. In the first place, they, as we now know, estimated Grouchy’s force at only half its strength,—they never, it must be remembered, actually saw it; and in the second place, Grouchy might well be detained by Thielemann at and about Wavre until the battle of Waterloo had been won. If, however, Grouchy had been observed marching from the Dyle directly on their columns _en route_ for Planchenoit, the Prussian commanders almost certainly would have been compelled to halt and to give him battle. And this they must have done even although they might have been satisfied that their forces were superior in numbers. A smaller force, if it is directed on the line of march of a larger one, almost inevitably must detain it. 7. The complete ruin which overtook the French army at Waterloo is to be attributed mainly to the unexpected appearance and vigorous attack of Zieten’s Corps at the close of the day, when the French had become thoroughly exhausted, and when, owing to the darkness, it was impossible for the Emperor to accomplish anything in the way of rallying them or making new dispositions. The English had certainly won a great success in routing the Imperial Guard; but they were not strong enough to drive the French army from the field, even with the assistance which Bülow and Pirch I. afforded on the side of Planchenoit. They had cleared their front of the enemy from Hougomont to the turnpike; but they were in no condition to attack the strong position of the French, defended by the troops of the 2d Corps, and crowned with many and powerful batteries. The French centre, Müffling tells us,[780] remained immovable after their right wing was in full retreat, and it was not until some of Zieten’s batteries, which had been brought over to the west of La Haye Sainte, opened fire, that it began to retire. Then Wellington ordered his whole line to advance. But it was a very thin line indeed, consisting, as Müffling says, only of small bodies, of a few hundred men each, and at great intervals from each other. Müffling goes on to say:—[781]