In short, the importance of seizing upon the means that presented themselves for materially retarding, if not of completely frustrating, the co-operation of the principal portion of the Prussian forces, was of so vital a nature, that the French Emperor would have been justified in detaching the whole of LOBAU's Corps, along with the Cavalry already mentioned, under an experienced and enterprising General, such as LOBAU himself, to operate against the Prussians whilst these were occupied in passing the Defiles which led to his Right Flank. None of those troops were engaged with the Anglo-Allied Army during any part of the day; so that, without diminishing the numbers actually opposed to the latter, they might have been detached in the manner suggested: instead of remaining, as was the case, drawn up _en potence_ on the immediate Field of Action, to be attacked by the Prussians, who were permitted to pass the Defiles without interruption, to collect their forces under cover of the Wood of Paris, to debouch from the latter successively and at their leisure, and to organise their movements of attack in perfect security, and with the most systematic order and regularity. CHAPTER XI. NAPOLEON, having taken the precaution of posting a Cavalry Corps of Observation upon his Right Flank, no longer delayed sending the Order to NEY for the commencement of the Grand Attack upon the Centre and Left Wing of the Anglo-Allied Army. About the same time, WELLINGTON, considering that some of the Battalions along the Right Wing of his Front Line were too much exposed to the Enemy's cannonade, which had from the commencement been principally directed against them, and which was now conducted with increased vigour, withdrew them more under shelter of the crest of the ridge. It might then be about half past one, or perhaps a quarter before two o'clock. The simultaneous advance of D'ERLON's four Divisions of Infantry, amounting to more than 16,000 men, was grand and imposing. As the heads of the Columns cleared their own line of Batteries ranged along the crest of the intervening ridge, and as the points on which they were directed for attack opened out to their view, loud and reiterated shouts arose from their ranks of "_Vive l'Empereur!_" which, as the masses began to descend the exterior slope of their position, were suddenly drowned in the roar produced by the discharge of seventy four pieces of French cannon over their heads. The effects of the latter upon PICTON's Division, and upon BYLANDT's Dutch-Belgian Brigade, which, as before stated, was deployed upon the exterior slope of the Anglo-Allied position, were severely felt.