If he could destroy the existing Coalition forces south of Brussels before they were reinforced, he might be able to drive the British back to the sea and knock the Prussians out of the war.

The Duke of Wellington expected Napoleon to try to envelop the Coalition armies, a maneuver that he had successfully used many times before,[9] by moving through Mons to the south-west of Brussels.

Only very late on the night of 15 June was Wellington certain that the Charleroi attack was the main French thrust, and he duly ordered his army to deploy near Nivelles and Quatre Bras.

Lieutenant-General Zieten's I Corps rearguard action on 15 June held up the French advance, allowing Blücher to concentrate his forces in the Sombreffe position, which had been selected earlier for its good defensive attributes.

Napoleon's original plan for 16 June was based on the assumption that the Coalition forces, which had been caught napping, would not attempt a risky forward concentration, and he intended, therefore, to push an advance guard as far as Gembloux, to feel for and ward off Blücher.

[12] In pursuance of this object Ney, to whom III Cavalry Corps (Kellermann) was now attached, was to mass at Quatre Bras and push an advanced guard 10 kilometres (6.2 mi) northward of that place, with a connecting division at Marbais to link him with Grouchy.

Napoleon now awaited further information from his wing commanders at Charleroi, where he massed the VI Corps (Lobau), to save it, if possible, from a harassing countermarch, as it appeared likely that it would only be wanted for the march to Brussels.

[12] The French Armee du Nord (Army of the North) was commanded by veteran officers and headed by Napoleon himself, who had won dozens of battles.

In equipment and supply, the French were well set with both, although the Guard units had to suffer standard weapons, and the Army of the North had more cavalry than their opponents throughout the four days of battle that would follow and end at Waterloo.

[15] The Prussians were not caught napping and set up a series of artillery/cavalry outposts whereby the cavalry patrolled the front and raced back to the artillery which would fire cannon in a prearranged signal.

The plan of separation of opposing armies and defeat in detail was an old and favored stratagem of Napoleon's, dating back to his operations in Italy, and had been the deciding factor in his campaigns in Austria, and in his battles with the Fifth Coalition.

William Siborne, writing from eyewitness accounts, records it thus: "Upon a calculation being made, however, of the time which would elapse ere the Duke would be able to collect the requisite force for undertaking this operation, and of the possibility of Blucher being defeated before it could be carried into effect, it was considered preferable that Wellington should, if practicable, move to the support of the Prussian Right by the Namur road.

The latter having expressed his confident expectation of being enabled to afford the desired support, as also of his succeeding in concentrating, very shortly, a sufficient force to assume the offensive, rode back to Quatre Bras."

Napoleon delayed his attack until about 14:30 when he heard cannon fire coming from the direction of Quatre Bras, and thus knew that his left flank was secure.

This delay also gave Gérard's IV Corps more time to deploy as it had only recently arrived in Fleurus from the south-west, and had an important role to play in Napoleon's plan of attack on Ligny.

A renewed attack by Vandamme's troops led to a bitter fight in which the Prussians lost approximately 2,500 men and possession of Saint-Amand-la-Haye.

The Prussian second lieutenant, Gerhard Andreas von Garrelts, later gave an eye-witness account of the agonies of the Belgian civilian population, caught unexpectedly in the centre of battle: Ligny stood half on fire, locked in bright flames [...] on this occasion we found we were in a house, where all windows were destroyed, two old people, a man and a woman, showing no emotion and dazed sat at the hearth, without moving, his elbows on his knees and his head supported by his hands; the vision made us cry!

At about the same time Vandamme on the left French flank sighted a force of twenty to thirty thousand men advancing on Fleurus, which he incorrectly took to be enemy troops.

Vandamme's III Corps received unexpected support from Duhesme's Young Guard and the Prussians were thrown back to their original positions.

It was now that Blücher received a message that Wellington was heavily engaged fighting Ney's left wing of the French army and, therefore, could on no account send support to Ligny.

At about 19:45 a crashing salvo of 60 guns gave the signal for a combined assault to be delivered by Gerard and the Guard, with Milhaud's cavalry moving on their right flank.

[27] However Blücher's worn-out soldiers at that section of the line could not withstand the concentrated impact of Napoleon's choicest troops, combined with a flanking movement by a division of French infantry under cover of the darkness, and at around 20:30 the Prussian centre at Ligny was overwhelmed.

[30][27] In the words of William Siborne: The Prussian infantry compelled to evacuate Ligny, effected its retreat in squares, in perfect order, though surrounded by the enemy, bravely repelling all further attacks, made in the repeated but vain attempts to scatter it in confusion.

Glover also writes "A retreat on Gembloux by the entire army would be the obvious course of action, except that this would lead to a complete break of contact with Wellington.

Ignoring all the false courses of action that traditional practices and misplaced prudence might have suggested in such a case, he followed his common sense and decided to turn toward Wellington on the 18th, preferring to abandon his own line of communications rather than adopt half-measures.

On the Prussian right, Lieutenant-General Zieten's I Corps retreated slowly with most of its artillery, leaving a rear-guard close to Brye to slow any French pursuit.

[38] Von Bülow's IV Corps, which had not been engaged at Ligny, moved to a location south of Wavre and set up a strong position on which the other elements of the Prussian army could reassemble.

It is a battle which 78,000 men lost to 75,000 by very slight tipping of the scales, after a long struggle, and without any truly glorious results for the victor, since his trophies consisted of only 21 guns and perhaps a few thousand prisoners.8,000 troops fled to Liege and Aix-la-Chapelle.

[38] Wellington anticipated that Napoleon would then come against him at Quatre Bras, so he spent 17 June retreating northwards to a defensive position he had personally reconnoitred the previous year at Mont-Saint-Jean, a low ridge south of the village of Waterloo and the Forest of Soignes.

The French pursued Wellington to Waterloo but managed only to defeat a small cavalry rearguard in an action at Genappe before torrential rain set in for the night.