Upon the 15th June, the French army was in motion in every direction. Their advanced-guard of light troops swept the western bank of the Sambre clear of all the allied corps of observation. They then advanced upon Charleroi, which was well defended by the Prussians under General Ziethen, who was at length compelled to retire on the large village of Gosselies. Here his retreat was cut off by the second division of the French army, and Ziethen was compelled to take the route of Fleurus, by which he united himself with the Prussian force, which lay about the villages of Ligny and St. Amand. The Prussian general had, however, obeyed his orders, by making such protracted resistance as gave time for the alarm being taken. In the attack and retreat, he lost four or five guns, and a considerable number in killed and wounded.
By this movement the plan of Napoleon was made manifest. It was at once most scientific and adventurous. His numbers were unequal to sustain a conflict with the armies of Blucher and Wellington united, but by forcing his way so as to separate the one enemy from the other, he would gain the advantage of acting against either individually with the gross of his forces, while he could spare enough of detached troops to keep the other in check. To accomplish this masterly manœuvre, it was necessary to push onwards upon a part of the British advance, which occupied the position of Quatre-bras, and the yet more advanced post of Frasnes, where some of the Nassau troops were stationed. But the extreme rapidity of Napoleon's forced marches had in some measure prevented the execution of his plan, by dispersing his forces so much, that at a time when every hour was of consequence, he was compelled to remain at Charleroi until his wearied and over-marched army had collected.
In the meantime, Ney was detached against Frasnes and Quatre-bras, but the troops of Namur kept their post on the evening of the 15th. It is possible the French maréchal might have succeeded had he attacked at Frasnes with his whole force; but hearing a cannonade in the direction of Fleurus (which was that of Ziethen's action,) he detached a division to support the French in that quarter. For this exercise of his own judgment, instead of yielding precise obedience to his orders, Ney was reprimanded; a circumstance curiously contrasted with the case of Grouchy, upon whom Napoleon laid the whole blame of the defeat at Waterloo, because he _did_ follow his orders precisely, and press the Prussians at Wavre, instead of being diverted from that object by the cannonade on his left.