The Prussians had lost twenty thousand men, missing, wounded, and dead, and it required vigorous treatment to restore Blücher. But all night the army marched, and in the morning Bülow, having found his direction, was near Beauderet and Sauvinières, within easy reach at Gembloux. The retreat continued throughout the seventeenth. It was a move of the greatest daring, since the line was over a broken country almost destitute of roads, and, the old base of supplies having been abandoned, the men had to starve until Gneisenau could secure another by way of Louvain. The army bore its hardships well; there was no straggling or demoralization, and the splendor of success makes doubly brilliant the move which confounded Napoleon's plans. Never dreaming at first that his foe had withdrawn elsewhere than along his natural line of supply toward Liège, the Emperor considered the separation of the two allies as complete, and after carefully deliberating throughout the long interval he allowed for collecting his troops and giving them a thorough rest, he determined to wheel, join Ney, and attack Wellington, wherever found. It was serious and inexplicable slackness which he showed in not taking effective measures to determine immediately where his defeated enemy was. Being, nevertheless, well aware of the Prussian resources and character, he made up his mind to detail Grouchy, with thirty-three thousand men, for the purpose of scouring the country toward Liège at least as far as Namur. Then, to provide for what he considered a possible contingency,--namely, that which had actually occurred,--this adjunct army was to turn north, and hasten to Gembloux, in order to assure absolutely the isolation of Wellington; in any and every case the general was to keep his communications with Napoleon open.
It was eight in the morning of the seventeenth when Napoleon issued from his quarters at Fleurus. Flahaut was waiting for the reply to an inquiry which he had just brought from Ney concerning the details of Ligny. The Emperor at once dictated a despatch, the most famous in the controversial literature of Waterloo, in which his own achievements were told and Ney was blamed for the disconnected action of his subordinates the previous day; in particular the marshal was instructed to take position at Quatre Bras, "as you were ordered," and d'Erlon was criticized for his failure to move on St. Amand. The wording of the hastily scribbled order to the latter he had probably forgotten; it was: "Portez-vous ... à la hauteur de Ligny, et fondez sur St. Amand--ou vice versa; c'est ce que je ne sais bien." ("Betake yourself ... to the heights of Ligny, pounce on St. Amand--or the reverse; I am not quite sure which.") Further, the Emperor now declared that, had Ney kept d'Erlon and Reille together, not an Englishman would have escaped, and that, had d'Erlon obeyed his orders, the Prussian army would have been destroyed. In case it were still impossible to seize Quatre Bras with the force at hand, Napoleon would himself move thither. Then, entering a carriage, he drove to Ligny; Lobau was ordered at once to Marbais, on the road to Quatre Bras. After haranguing the troops and prisoners, Napoleon was informed, about noon, that Wellington was still in position. At once a second order was sent, commanding Ney to attack; the Emperor, it ran, was already under way to Marbais. This was not quite true, for while he was giving detailed instructions to Grouchy before parting, that general had seemed uneasy, and had finally pleaded that it would be impossible further to disorganize the Prussians, since they had so long a start. These scruples were peremptorily put down, and the chief parted amicably from his subordinate, but with a sense of uneasiness, lest he had left nice and difficult work in unwilling hands. Scouts soon overtook him, and expressed doubt as to the Prussians having gone to Namur. In case they had not, Grouchy must act cautiously. Accordingly, positive instructions were then dictated to Bertrand, and sent to Grouchy, whose movements were now doubly important. The latter general was to reconnoiter toward Namur, but march direct to Gembloux; his chief task was to discover whether Blücher was seeking to join Wellington or not. For the rest, he was free to act on his own discretion.