The Waterloo campaign commenced with a pre-emptive attack by the French Army of the North under the command of Napoleon Bonaparte. The first elements of the Army of the North moved from their peacetime depots on 8 June to their rendezvous point just on the French side of the Franco-Belgian border. They launched a pre-emptive attack on the two Coalition armies that were cantoned in Belgium—the Anglo-allied army under the command of the Duke of Wellington, and a Prussian army under the command of Prince Blücher.
Hostilities commenced shortly after the French advanced guard crossed the border and encountered the first Coalition outposts manned by soldiers of the Prussian I Corps (Zieten's) around 03:30 on 15 June. For the rest of the day the I Corps engaged in a fighting retreat against the overwhelming force of the French Army of the North. By midnight of 15/16 June the French had advanced north and through Charleroi and in doing so successfully crossed the river Sambre, the only significant river between the French army and Brussels.
At 19:00 on 15 June Marshal Ney, who had ridden up from Paris, met Napoleon near Charleroi, at the point where the road to Fleurus branches off from the one to Brussels. He was ordered to take command of the left wing of the Army of the North and press north up the Charleroi–Brussels road towards the Anglo-allied army and "drive back the enemy" while Napoleon would advance up the Fleurus road and do the same to the Prussians. The advance up the two roads continued until darkness, but slowed during the evening as Coalition troops fell back on reinforcements. The French planned to renew their advance on 16 June, while the Anglo-allied army planned to check them at Quatre Bras, and the Prussian army at Ligny.
Prelude
On 1 March 1815 Napoleon Bonaparte landed in France after his escape from Elba, he marched on Paris. When it became clear that the troops sent to arrest him would not do so, and his arrival in the capital was imminent, Louis XVIII fled.
The representatives of the other European powers assembled at the Congress of Vienna issued a declaration outlawing Napoleon and each agreed to place armies of at least 150,000 in the field to oppose him.
The Coalition Powers agreed on a coordinated invasion of France to start on 1 July 1815. To this end it was agreed that: Britain and Prussia would assemble their armies in Belgium (a territory recently acquired by United Kingdom of the Netherlands) The Russians would assemble an army and advance through Germany towards the French frontier The Austrians would assemble two armies and advance on the French frontiers The troops of Bavaria, Baden, Wurtemberg, and Hesse, would assemble their troops on the upper Rhine under the command of the Prince of Württemberg.
As soon as it became apparent that the Coalition Powers were determined to use force against him, Napoleon started to prepare for war. He had a choice of two strategies: either to assemble his forces in and around Paris and defeat the Coalition Powers as they attempted to invest the city, or to launch a pre-emptive attack and destroy each of his enemies' armies before they could combine. He chose the latter strategy and decided to attack the two Coalition armies in Belgium which were cantoned close to the borders of France.
The Prussian army, commanded by Prince Blücher, was cantoned south east of Brussels with its headquarters in Namur. The Anglo-allied army, commanded by the Duke of Wellington, was cantoned south west of Brussels with its headquarters in Brussels. Wellington's army included contingents from the British Army (including the KGL), Hanover (their king was also the king of Britain), Brunswick (until very recently closely associated with Hanover and hence the British), the Kingdom of the Netherlands (Dutch and Belgian troops), and Nassau (had close dynastic ties with the Netherlands and part of the territory had until very recently been ruled by the King of the Netherlands).
Napoleon's plan of campaign Having decided to attack the Coalition forces in what is now Belgium, Napoleon had several strategies open to him and, although the Coalition commanders knew that they might well be attacked, they were uncertain as to the timing and line of advance that Napoleon would choose.
From his spies Napoleon knew how widely the Coalition forces were spread over the Low Countries. He was aware that the two armies had two distinct and divergent bases, and were commanded by two generals differing in character. His only chance of success lay in swift marches and crushing victories. He had to defeat his foes in detail, and though his aggregate force was weaker than their aggregate force, he had to be always the stronger at the point of contact.
Napoleon argued in conference with his generals that he must not attack between the rivers Moselle and the Meuse, because that course would allow Wellington to join Blücher without molestation; nor must he attack between the rivers Sambre and Scheldt, because in that case Blücher would be able to effect a junction with Wellington. Nor, and for similar reasons, did he deem it prudent to descend the Meuse and attack the city of Namur.
Napoleon noticed that the Coalition armies would require the longest time to concentrate on their inner flanks, and he decided to attack between the Sambre and the Meuse, to wedge himself in between them, crushing any divisions trying to obstruct his progress. Having the advantage, he planned to manoeuvre rapidly on interior lines, and defeat each army in succession before they could join forces.
Napoleon had selected for the line of his main operations the direct road to Brussels, by Charleroi—the road on which Wellington's left wing, and Blücher's right wing rested. As the Prussians' front line covered Charleroi and the French territory immediately to the south of Charleroi, and the Anglo-Allies' most advanced outpost was further up the Charleroi–Brussels road at Frasnes-lez-Gosselies (about north of Charleroi), he planned to first overcome the Prussian army, and then attack the Anglo-allied troops before they could deploy properly.
Napoleon's grand object was to prevent the two armies combining and destroy them both; to establish himself in Brussels; to arouse the dense population in Belgium (of which a vast proportion secretly adhered to his cause); to re-annex the country to the French Empire; to excite the desertion of the Belgian soldiery from the service of the Netherlands; to discourage invading armies from crossing the Rhine; perhaps also to enter into negotiations — and most important of all, to gain time to gather and train reinforcements from France.
Start of operations (8–12 June)
Advance of the French Army of the North The French IV Corps (Gérard's) left Metz on 6 June, with orders to reach Philippeville by 14 June. The Imperial Guard (commanded by Drouot) began its march from Paris on 8 June, and reached Avesnes on 13 June, as did the VI Corps (Lobau's) from Laon. The I Corps (d'Erlon's) from Lille, II Corps (Reille's) from Valenciennes, and III Corps (Vandamme's) from Mézières, likewise arrived at Maubeuge and Avesnes on 13 June. The IV Corps of Reserve Cavalry (Milhaud's) concentrated upon the Upper Sambre.
Napoleon joins the army The junction of the several corps on the same day, and almost at the same hour (with the exception of the IV, which joined the next day), displayed the usual skill of Napoleon in the combination of movements. Their leaders congratulated themselves upon these auspicious preparations, and upon finding the "Grand Army" once more assembled in "all the pomp and circumstance of glorious war": the appearance of the troops, though fatigued, was all that could be desired; and their enthusiasm was at the highest on hearing that the Emperor himself, who had left Paris at 03:00 on 12 June and passed the night at Laon, had actually arrived amongst them.
Upon the following day, the French Army bivouacked on three different points: The left wing, consisting of the I Corps (d'Erlon's) and the II Corps (Reille's), and amounting to about 44,000 men, was posted on the right bank of the Sambre at Solre-sur-Sambre. The centre, consisting of the III Corps (Vandamme's) and the VI Corps (Lobau's), of the Imperial Guard, and of the Cavalry Reserves (I (Pajol's), II (Exelmans's), III (Kellermann's)) amounting altogether to about 60,000 men, was at Beaumont, which was made the headquarters. The right wing, composed of the IV Corps (Gerard's) and of a division of heavy cavalry, amounting altogether to about 16,000 men, was in front of Philippeville.
The army's bivouacs were set up with a view to conceal their fires from observation by Coalition pickets and scouts.
The Army received through the medium of an ordre du jour (order of the day), a spirit-stirring appeal to his army from their commander and emperor (see "Proclamation on the Anniversary of the Battles of Marengo and Friedland, 14 June 1815").
13 June
French deception and limited Coalition intelligence Napoleon had effectually concealed the movements of several corps, and their concentration on the right bank of the Sambre, by strengthening his advanced posts, and displaying an equal degree of vigilance and activity, along the whole line of the Belgian frontier.
However, during the night of 13 June, the light reflected upon the sky by the French fires was noticed by observation outposts of the Prussian I Corps (Zieten's). The Prussians realised that these fires appeared to be in the direction of Walcourt and Beaumont, and also in the vicinity of Solre-sur-Sambre.
Further reports from spies and deserters concurred by saying that Napoleon was expected to join the French army on that evening; that the Imperial Guard and the II Corps had arrived at Avesnes-sur-Helpe ("Avesnes") and Maubeuge; also that, at 13:00 four French battalions had crossed the river at Solre-sur-Sambre, and occupied Merbes-le-Château; that later in the night the French had pushed forward a strong detachment as far as Sars-la-Buissière; and lastly that an attack by the French would take place on 14 or 15 June.
14 June
First news of the French concentration On 14 June, the Dutch-Belgian Major-General van Merlen (who was stationed at Saint-Symphorien near Mons), and who commanded the outposts between the Saint-Symphorien and Binche which formed the extreme right of the Prussians, ascertained that French troops had moved from Maubeuge and its vicinity by Beaumont, towards Philippeville. Also that there was no longer any hostile force in his front, except a picket at Bettignies, and some National Guards in other villages. He forwarded this important information to the Prussian General Steinmetz, on his left, with whom he was in constant communication. Steinmetz despatched this information to General Zieten at Charleroi.
The Prussian General Pirch II, whose 2nd Brigade was posted on the left of Steinmetz, also sent word to Zieten that he had received information through his outposts that the French army had concentrated in the vicinity of Beaumont and Merbes-le-Château; that their army consisted of 150,000 men, and was commanded by General Vandamme, Prince Jerome Bonaparte, and other distinguished officers; that since the previous day all crossing of the frontier had been forbidden by the French under pain of death; and that a French patrol had been observed that day near Biercée, not far from Thuin.
During the day, frequent accounts were brought to the troops of Prussian I Corps (Zieten's)—generally collaborating earlier reports—by the country people who were seeking some place of safety for their cattle. Their stories confirmed the above, and also that Napoleon, and of his brother Jerome had arrived.