At ten o’clock that evening Grouchy wrote to the Emperor from Gembloux a letter[482] which seemed to indicate that he comprehended, at least to a certain extent, the nature of his task. He says that it appeared to him that the Prussians had passed through Sauvenières, where his (Grouchy’s) cavalry now have arrived, and that, at Sauvenières, they had divided into two columns, one taking the road to Wavre, by Sart-à-Walhain, and the other that to Perwez, a town on the way to Maestricht. Grouchy then goes on to say:— “One may perhaps infer that a part is going to join Wellington, and that the centre, which is the army of Blücher, is retiring on Liége; another column with artillery has effected its retreat on Namur. Exelmans has been ordered to send this evening six squadrons to Sart-à-Walhain and three to Perwez. “According to their reports, _if the mass of the Prussians is retiring on Wavre, I shall follow them in that direction, in order that they may not be able to gain Brussels, and to separate them from Wellington_.[483] “If, on the contrary, my information proves that the principal Prussian force has marched on Perwez, I shall direct myself on that city in pursuit of the enemy.” That Marshal Grouchy understood something of the nature of the task before him is apparent from this despatch. But when he says that his object in following the mass of the Prussians in the direction of Wavre is to prevent their gaining Brussels, he is plainly beside the mark. No movement of his from Gembloux to Wavre or in the direction of Wavre could possibly hinder a force at Wavre from marching on Brussels. When he declares that his object in proceeding in the direction of Wavre would be to separate the Prussians from Wellington, he must be understood to mean the direction of Wavre, as contradistinguished from the direction of Perwez,—that is, in other words, if the Prussians go north instead of east he will also go north instead of east. And as he had abundance of cavalry, there was certainly no reason, now that he had cause, as he says he had, to suspect that a part of the Prussians had gone to Wavre, with the intention of uniting with Wellington, why he should not have reconnoitred to his left the next morning and ascertained the facts.