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] “But the moment he learnt that Blücher had turned towards the Dyle, which must have happened in Gembloux in the night between the 17th and 18th, the idea must have shot at once into his mind that this could only be in order to join Wellington, for one does not leave one’s natural line of retreat without reason. From that moment he had to consider it his duty, not to lie at the heels of Blücher’s rear-guard, but to get between him and Bonaparte, in order to be able to throw himself in front of Blücher in case he wanted to march off to his right. According to this, he would have to turn from Gembloux to the Dyle by the shortest road, &c.” Says Charras:—[586]