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.