NAPOLEON's instructions to GROUCHY were extremely simple and concise: "Pursue the Prussians, complete their defeat by attacking them as soon as you come up with them, and never let them out of your sight. I am going to unite the remainder of this portion of the Army with Marshal NEY's Corps, to march against the English, and to fight them if they should hold their ground between this and the Forest of Soignies. You will communicate with me by the paved road which leads to Quatre Bras." No particular direction was prescribed, because the Emperor was totally ignorant of the real line of the Prussian retreat. At the same time he was strongly impressed with the idea that BLÜCHER had retired upon Namur and Liege, with a view to occupy the line of the Meuse, whence he might seriously endanger the Right of the French Army, as also its main line of operation, should it advance upon Brussels. GROUCHY did not hesitate to remark to the Emperor, that the Prussians, having commenced their retreat at ten o'clock the previous night, had gained several hours' start of the troops with which he was to follow them; that although the reports received from the Advanced Cavalry conveyed no positive information as to the direction in which the great mass of the Prussian Army had effected its retreat, appearances as yet seemed to justify the supposition that BLÜCHER had fallen back upon Namur; and that as he would thus have to pursue in a direction contrary to that which NAPOLEON was himself going to take, with very little chance of being able to prevent the execution of any dispositions the Prussians might have resolved upon when quitting the Field of Battle, he begged to be allowed to follow the Emperor in his projected movement upon Quatre Bras. NAPOLEON declined to entertain this proposition, repeated the Order he had already given to him, adding that it rested with him (GROUCHY) to discover the route taken by the Prussians, whose defeat he was to complete by attacking them the moment he came up with them; while he himself would proceed to fight the English. * * * * * The Order was immediately given for the advance of the troops previously assembled near Marbais, preceded by SUBERVIE's Division of Light Cavalry, as Advanced Guard. By the time they reached Quatre Bras, which was about two o'clock, the whole of WELLINGTON's Infantry had crossed the Genappe, and was retiring along the high road to Brussels, protected by the Cavalry, which was now pressed by the French, in the manner described in the preceding Chapter.