So far, we have followed the retreat of the Prussians northwards from their defeat at Ligny. With the exception of the rearguard, they were all disposed by the evening of Saturday the 17th in an orderly fashion round the little town of Wavre. We have also followed the methodical but tardy and ill-conceived pursuit in which Grouchy felt out with his cavalry to discover the line of the Prussian retreat, and continued to be in doubt of its nature at least until midnight, and probably until even later than midnight, in that night between Saturday the 17th, evening, and Sunday the 18th of June. We have further seen that during the morning of Sunday the 18th of June he was taking no dispositions for a rapid pursuit, but, being now convinced that the Prussians merely intended a general retreat upon Brussels, proposed to follow them in order to watch that retreat, and, if possible, to shepherd them eastwards. He wrote, as we have just said, to the Emperor in the course of that morning of the Sunday, announcing that he meant to mass his troops at Wavre by nightfall, and asking for orders for the next day. What the Prussians were doing during that Sunday morning when Grouchy was so quietly and soberly taking for granted that they could not or would not rejoin Wellington, and was so quietly shielding his own responsibility behind the Emperor's orders, we shall see when we come to talk of the action itself--the battle of Waterloo. Meanwhile we must return to the second half of the great strategic move, and watch the retreat of the Duke of Wellington during that same Saturday, and the stand which he made on the ridge called "the Mont St Jean" by the nightfall of that day, in order to accept battle on the Sunday morning. An observer watching the whole business of that Saturday from some height in the air above the valley of the Sambre, and looking northwards, would have seen on the landscape below, to his right, the Prussians streaming in great parallel columns upon Wavre from the battlefield of Ligny. He would have seen, scattered upon the roads, small groups of mounted men, here in touch with the last files of a Prussian column, there lost and wandering forward into empty spaces where no soldiers were. These were the cavalry scouts of Grouchy. South of these, and far behind the Prussian rear, separated from them by a gap of ten miles, a dense body of infantry, drawn up in heavy columns of route, was the corps commanded by Grouchy.