Hence, at or soon after 10 P.M., he issued his orders to his corps-commanders to march in the morning to Sart-à-Walhain. Vandamme,[571] whose corps had bivouacked somewhat in advance of Gembloux, was to start at 6 A.M. It was to be preceded in the march by Exelmans’ cavalry, the bulk of which was at Sauvenières. Gérard,[572] whose troops were in and about Gembloux, was to follow with his corps at 8 A.M. Pajol[573] was ordered from Mazy on the Namur road, where he then was, taking with him the division of Teste, to Grand Leez, where he would receive further orders.
Then, at 2 A.M., Grouchy writes to the Emperor to inform him that he was intending to march on Sart-à-Walhain,[574] but without indicating his ulterior course.
During the early morning hours, however, information was received[575] which removed his doubts as to the direction of the Prussian retreat, for we find him writing to Pajol[576] “at daybreak,” as follows:—
“The movement of retreat of Blücher’s army appears to me very clearly to be upon Brussels.”[577]
Marshal Grouchy, therefore, at daybreak,—which in Belgium at that season of the year is at least as early as 3.30 A.M.,—for the sun rises at 3.48 A.M.,—had come to the conclusion that Blücher was retiring on Brussels by way of Wavre. Yet he still adhered to his plan of marching on Sart-à-Walhain, although that place had been chosen the evening before as the first stage in the next day’s march because he had then been in doubt as to whether his ultimate movement would be in the direction of Wavre or in that of Perwez.[578] Moreover, although he had come to the conclusion that the Prussians were retiring on Wavre, towards the English, which made promptness and celerity on his part of the very first importance, he did not change the very late hours he had fixed for the march of the next morning. In fact, even these hours were not adhered to. Exelmans,[579] who preceded the column, did not start till 7.30 A.M.; Vandamme,[580] who came next, did not move until 8 A.M.; and it was not until 9 A.M. that Gérard’s[581] corps got through the town of Gembloux, and was in full march for Sart-à-Walhain. And yet no one knew better than Marshal Grouchy that the Prussians had many hours the start of him, and that if he was going to do anything that day to prevent them from joining Wellington, there was no time to be lost.
There is no difference of opinion among the Continental[582] authorities as to Marshal Grouchy’s true course on this morning. As soon as he had arrived at the conclusion that the Prussians were retiring on Wavre, which was, as we have seen, between 3 and 4 A.M., he should have changed his evening orders entirely; he should have begun his march at once, and should have directed it to the bridge of Moustier. (See Map 9.)
Says Jomini:—[583]
“The Marshal should not, then, have hesitated; he should at daybreak on the 18th have marched with all speed on Moustier with Exelmans, Vandamme and Gérard, directing Pajol’s cavalry and Teste’s division on Wavre, in pursuit of the enemy’s rearguard.
“Being able to reach Moustier by ten o’clock,[584] he could have then forwarded his infantry on Wavre by Limale, pushing Exelmans’ dragoons on St. Lambert, or else have marched to Lasne himself.”
Says Clausewitz:—[585]