As it was, Napoleon's own delay in crossing the Sambre made Wellington's mistake and tardiness bear no disastrous fruit. The Duke failed to succour the Prussians. His troops, scattered all over Western Belgium, did not come up in time to prevent the defeat of his allies at Ligny. But he held his own at Quatre Bras; and in the final battle, forty-eight hours later, the genius with which he handled his raw troops upon the ridge of Mont St Jean wiped out and negatived all his strategical misconceptions of the previous days. From this confusion, this partial delay and error upon Napoleon's part, this ignorance upon Wellington's of what was toward, both of which marked Thursday the 15th, we must turn to a detailed description of that morrow, Friday the 16th, which, though it is less remembered in history than the crowning day of Waterloo, was, in every military sense, the decisive day of the campaign. We shall see that it was Napoleon's failure upon that Friday completely to defeat, or rather to destroy, the Prussian force at Ligny--a failure largely due to Wellington's neighbouring resistance at Quatre Bras--which determined the Emperor's final defeat upon the Sunday at Waterloo. III THE DECISIVE DAY FRIDAY THE 16TH OF JUNE QUATRE BRAS AND LIGNY We have seen what the 15th of June was in those four short days of which Waterloo was to be the climax. That Thursday was filled with an advance, rapid and unexpected, against the centre of the allied line, and therefore against that weak point where the two halves of the allied line joined, to wit, Charleroi and the country immediately to the north of that town and bridge. We have further seen that while the unexpectedness of the blow was almost as thorough as Napoleon could have wished, the rapidity of its delivery, though considerable, had been less than he had anticipated. He had got by the evening of the day not much more than three-quarters of his forces across the river Sambre, and this passage, which was mapped out for completion before nightfall, straggled on through the whole morning of the morrow,--a tardiness the effects of which we shall clearly see in the next few pages. Napoleon's intention, once the Sambre was crossed, was to divide his army into two bodies: one, on the left, was to be entrusted to Ney; one, on the right, to Grouchy. A reserve, which the Emperor would command in person, was to consist in the main of the Imperial Guard. The left-hand body, under Ney, was to go straight north up the great Brussels road.