The Emperor left Paris on the night between the 11th and 12th of June, as some writers declare "to measure himself against Wellington." The Imperial Guard had commenced its march on the 8th, and all the different corps of the army were in motion towards Maubeuge and Phillipville. When he had made known his intention of commencing the war, Caulaincourt solicited the favor of attending him. "If I do not leave you at Paris" answered Napoleon, "on whom can I depend?" Even then he felt that it was not the Allies alone that he had to contend against; and when he had left Paris he seemed less apprehensive of the enemies before, than those he had left behind him. To Bertrand's wife he said, as he took her hand at departing, "Let us hope, Madame Bertrand, that we may not soon have to regret the Island of Elba."
Napoleon arrived at Vervins on the 12th of June and assembled and reviewed at Beaumont on the 14th, the whole of the army which had been prepared to act immediately under his own orders. They had been most carefully selected, and formed, and it was, perhaps, the most perfect force, though far from the most numerous, with which he had ever taken the field. The returns showed that his army amounted to one hundred and twenty-two thousand four hundred men, with three hundred and fifty pieces of cannon. These included 25,000 of his Imperial Guard, 25,000 cavalry in the highest condition, and artillery admirably served. "The whole army was superb and full of ardor;" says Count Labedoyere, "but the Emperor, more a slave than could have been credited to recollections and old habits, committed the great fault of replacing his army under the command of its former chiefs, most of whom, notwithstanding their previous addresses to the King, did not cease to pray for the triumph of the Imperial cause; yet were not disposed to serve it with that ardor and devotion demanded by imperious circumstances. They were no longer men full of youth and ambition, generously prodigal of their lives to acquire rank and fame; but veterans, weary of warfare, who, having attained the summit of promotion, and being enriched by the spoils of the enemy, or the bounty of Napoleon, indulged no other wish, than the peaceable enjoyment of their good fortune under the shade of those laurels, they had so dearly acquired."
The Emperor reminded his soldiers, in a fiery proclamation issued on the 14th of June, that the day was the anniversary of the battle of Marengo and of Friedland. "Then, as after Austerlitz and Wagram" he said "we were too generous. We gave credit to the protestations and oaths of the princes whom we suffered to remain on their thrones. Now, however, having coalesced among themselves, they aim at the independence and the most sacred rights of France. They have commenced the most unjust of aggressions. Are we no longer the same men? Fools that they are! A moment of prosperity blinds them. The oppression and the humiliation of the French people are out of their power. If they enter France, there will they find their tomb. Soldiers! We have forced marches to make; battles to wage; perils to encounter; but with constancy the victory will be ours. The rights—the honor of the country—will be honored. For every Frenchman who has a heart, the moment has now arrived either to conquer or perish!"
The army of Blucher numbered at this time about 120,000 men. They communicated on their right with the left of the Anglo-Belgian army, under Wellington, whose headquarters were at Brussels. Blucher's forces extended along the line of the Sambre and the Meuse, occupied Charleroi, Namur, Givet, and Liege. The Duke of Wellington's host amounted in all to 75,000 men; his first division occupied Enghien, Brain-le-Compte and Nivelles, communicating with the Prussian right at Charleroi. The second division,—Lord Hills',—was cantoned in Halle, Oudenard and Gramont, together with the greater part of the cavalry. The reserve, under Sir Thomas Picton, was quartered at Brussels and Ghent. The English and Prussian commanders had thus arranged their troops with the view of being able to support each other, wherever the French might hazard their assault.
In the night between the 14th and 15th, scouts returned to the headquarters of the French, reporting that there was no movement among the invaders at Charleroi, Namur or Brussels, thus verifying the Emperor's belief that the plans for concealing the movements of his army during the last few days were successful. The Duke of Wellington, in a letter to Lord Bathurst, on the 13th, declared his disbelief in the report that Napoleon had joined the army, and it was not until the afternoon of the 15th that he possessed any knowledge of the position and intentions of Napoleon. On that day, an officer of high rank arrived at Wellington's headquarters in Brussels with the intelligence of Napoleon's decisive operations.
General Bourmont, a protegé of Ney, with Colonels Clouet and Villoutreys, and two other officers, had gone over to the enemy with all the Emperor's plans. Napoleon knew from Marshal Ney that Bourmont had shown some hesitation, and he had been backward in employing him. Bourmont, however, having given General Gerard his word of honor to serve the Emperor faithfully; and the general in question, whom Napoleon valued highly, having answered for his integrity, the Emperor consented to admit him into the service. He had covered himself with glory in 1814, and it was not to be expected that he would in 1815 go over to the enemy on the eve of a battle. A drum-major, who deserted from the French ranks some hours before General Bourmont and his two companions, was conducted under an escort to the headquarters of Blucher, at Namur, where he gave the first intelligence of Napoleon's intended attack. This was confirmed by Bourmont, Clouet and Villoutreys who added details with which the drum-major could not possibly have been acquainted.
Later on, in speaking of these traitors, Napoleon said, "Their names will be held in execration so long as the French people form a nation. This desertion increased the anxiety of the soldiers."
The Emperor immediately made those alterations in his plan of attack, as such unexpected treason rendered necessary, and then proceeded to carry out the details of his campaign. He had determined on first attacking the Prussians, as he believed Blucher would give him battle at once, in order to allow the English time to collect their forces. He believed also, that if the English army were attacked first, Blucher would more rapidly arrive to the support of the English than the latter were likely to do if the Prussians were first attacked.
Ney had been placed in command of 43,000 men, with orders to advance on the road to Brussels and make himself master of the position of Quatre-Bras, at all points, so as to prevent Wellington from supporting the Prussians. He was to march at daybreak, on the 16th, occupy the position and intrench himself.