Excelmans, arriving at Sauvenière at six o’clock in the evening, sent out Bonnemains’ Brigade (4th and 12th Dragoons) towards Sart à Walhain, and the 15th Dragoons towards Perwez, to reconnoitre. Scouts were also sent towards Tourinnes and Nil St Vincent. These scouts found a small Prussian rear-guard at Tourinnes, but they only watched the enemy for an hour, and then returned. Bonnemains brought his Brigade back to Ernage, where he bivouacked for the night. He had gathered information that the Prussians were retreating towards Wavre; and the 15th Dragoons also reported from the neighbourhood of Perwez to the same effect; so that Excelmans, at 10 P.M., knew with comparative certainty that the enemy were marching on Wavre.
Pajol, in the meantime, finding that he was mistaken in his conclusions as to the direction of the Prussian retreat, marched back from St Denis with Soult’s Light Cavalry and Teste’s Division to Le Mazy, the point from which he had started in the morning. Now, even if he had found that he was striking in a wrong direction, there can be no possible reason for his retreating to Le Mazy. He must have known that such a move, whether right or wrong, would have a very great influence on Grouchy’s plan; therefore, instead of marching all his forces back, he should have sent an aide-de-camp or galloper to find where the main body was, or to find Grouchy and get fresh instructions. Pajol exercised no discretion whatever in making such a move.
At 10 P.M., at Gembloux, Grouchy wrote the following despatch to the Emperor:—
“Gembloux, 17th June, 10 P.M.
“Sire,—I have the honour to report to you that I occupy Gembloux and that my Cavalry is at Sauvenière.[6] The enemy, about 30,000 strong, continues his retreat. We have captured here a convoy of 400 cattle, magazines and baggage.
“It would appear, according to all the reports, that, on reaching Sauvenière, the Prussians divided into two columns: one of which must have taken the road to Wavre, passing by Sart à Walhain; the other would appear to have been directed on Perwez.
“It may perhaps be inferred from this that one portion is going to join Wellington; and that the centre, which is Blucher’s army, is retreating on Liège. Another column, with artillery, having retreated by Namur,[7] General Excelmans has orders to push, this evening, six squadrons to Sart à Walhain, and three to Perwez. According to their report, if the mass of the Prussians is retiring on Wavre, I shall follow them in that direction, so as to prevent them from reaching Brussels, and to separate them from Wellington. If, on the contrary, my information proves that the principal Prussian force has marched on Perwez, I shall pursue the enemy by that town.
“Generals Thielemann and Borstel (?) formed part of the army which Your Majesty defeated yesterday; they were still here at 10 o’clock this morning,[8] and have announced that they have 20,000 casualties. They enquired on leaving, the distances of Wavre, Perwez, and Hannut. Blucher has been slightly wounded in the arm, but it has not prevented him from continuing to command after having had his wound dressed. He has not passed by Gembloux.—I am, with respect, Sire, Your Majesty’s faithful subject,
Marshal Count Grouchy.”
This despatch would not give Napoleon a very correct idea of the state of affairs. No mention was made by Grouchy of Pajol’s detachment, so the Emperor could only infer that Grouchy had all his cavalry together and all his infantry together. Mention should have been made, too, of the discovery that the Prussians had not retreated by the Namur road. So far as could be learnt from this despatch, only 30,000 Prussians had been accounted for. That Blucher had “not passed through Gembloux” would at once suggest that he had gone by some other road, not explored by Grouchy, with his main body.
Grouchy’s orders to his commanders for the next day, sent out at 10 P.M., showed that he still firmly believed that the Prussians were retreating on Liège, although in his despatch to Napoleon, he had recognised the possibility of their having taken the road to Wavre.
He ordered Excelmans’ Cavalry and Vandamme’s Corps to march to Sart à Walhain; Gérard’s Corps to follow Vandamme’s to Sart à Walhain, and the Seventh Cavalry Division to push on to Grand Leez; Pajol’s force to march from Le Mazy to Grand Leez. (Pajol had reached St Denis, half-way from Le Mazy to Grand Leez, on the 17th, so that he now had covered this ground twice.)
When Bonnemain’s reports to Excelmans reached Grouchy, he should have had no longer any doubts as to the true line of Blucher’s retreat. Towards half-past two in the morning, news from Walhain came in, to the effect that the peasants there had reported that about three Prussian Corps had passed through on the previous day, marching in the direction of Wavre. A glance at the map will show that Gembloux to Walhain is in the direction of Wavre, and not of Liège. Further, from information gathered by the peasants from Prussian stragglers and the gossips who seem to find a place in every army, the enemy were talking of the coming battle near Brussels. As to Grouchy’s thoughts, and the influence these reports had on him, it is difficult to find what train of reasoning he followed. He knew that Napoleon expected to fight Wellington near the Forest of Soignies: he knew, too, that the Emperor was anxious for him to prevent the Prussians from marching across to join the English, yet he did not consider the very great possibility that Blucher might rapidly join Wellington by a short flank march from Wavre. Had such a possibility entered his mind, he must have reflected on the best means of thwarting it, ere it became too late. Obviously his only move then was to make for the bridges at Moustier and Ottignies, viâ Saint Géry. By reaching the left bank of the Dyle (which he could easily do before Blucher), Grouchy could have either manœuvred to join Napoleon, when an addition of 33,000 troops must have overwhelmed Wellington, or he could have continued to pursue the Prussians, should it happen that he had been wrong in supposing that they were marching to join the English. It did not require extraordinary foresight or mental effort to realize how much more useful and how much more effective a move viâ St Géry and Moustier and the left bank of the Dyle would have been. If Grouchy was really as undecided as he appears to have been, as to the Prussian line of retreat, he should have had recourse to a movement which offered no doubtful advantages. A move across the Dyle by Moustier would have had a very great effect, and if the Prussians had really retreated on Liège, this movement of Grouchy’s would still have its advantages. He could have thrown his weight into the fight at Waterloo; Napoleon would not blame him for this assistance, if he knew that the Prussians were out of reach.
At 6 A.M. on the morning of the 18th, Grouchy sent another message to Napoleon, stating that further information had been received, which confirmed the news that Blucher was making for Brussels “viâ Wavre, so as to concentrate there, or to give battle after joining Wellington.” Grouchy told Napoleon in his message that he was “starting immediately for Wavre.” But he himself did not actually start until 9 A.M.
He ordered Vandamme to march at 6 A.M., and Gérard at 8 A.M. Now, at that time of year, it was light enough to march at 3.30 A.M., hence Grouchy wasted another valuable two and a half hours, when time was all-important. Again, there was no necessity to keep Gérard’s Corps waiting for Vandamme’s to get ahead, as there were no less than four roads from Gembloux towards Corbaix, and the two inner ones could easily have been used for this march.