Marshal Ney began the battle about two o'clock in the afternoon. He had at this time in hand about 16,000 infantry, nearly 2,000 cavalry, and 38 guns. The force which Napoleon nominally placed at his command exceeded 40,000 men. But more than one half of these consisted of the first French corps d'armee, under Count d'Erlon; and Ney was deprived of the use of this corps at the time that he most required it, in consequence of its receiving orders to march to the aid of the Emperor at Ligny. A magnificent body of heavy cavalry under Kellerman, nearly 5,000 strong, and several more battalions of artillery were added to Ney's army during the battle of Quatre Bras; but his effective infantry force never exceeded 16,000.

When the battle began, the greater part of the Duke's army was yet on its march towards Quatre Bras from Brussels and the other parts of its cantonments. The force of the Allies, actually in position there, consisted only of a Dutch and Belgian division of infantry, not quite 7,000 strong, with one battalion of foot, and one of horse-artillery. The Prince of Orange commanded them. A wood, called the Bois de Bossu, stretched along the right (or western) flank of the position of Quatre Bras; a farmhouse and building, called Gemiancourt, stood on some elevated ground in its front; and to the left (or east), were the inclosures of the village of Pierremont. The Prince of Orange endeavoured to secure these posts; but Ney carried Gemiancourt in the centre, and Pierremont on the east, and gained occupation of the southern part of the wood of Bossu. He ranged the chief part of his artillery on the high ground of Gemiancourt, whence it played throughout the action with most destructive effect upon the Allies. He was pressing forward to further advantages, when the fifth infantry division under Sir Thomas Picton and the Duke of Brunswick's corps appeared upon the scene. Wellington (who had returned to Quatre Bras from his interview with Blucher shortly before the arrival of these forces) restored the fight with them; and, as fresh troops of the Allies arrived, they were brought forward to stem the fierce attacks which Ney's columns and squadrons continued to make with unabated gallantry and zeal. The only cavalry of the anglo-allied army that reached Quatre Bras during the action, consisted of Dutch and Belgians, and a small force of Brunswickers, under their Duke, who was killed on the field. These proved wholly unable to encounter Kellerman's cuirassiers and Pire's lancers; the Dutch and Belgian infantry also gave way early in the engagement; so that the whole brunt of the battle fell on the British and German infantry. They sustained it nobly. Though repeatedly charged by the French cavalry, though exposed to the murderous fire of the French batteries, which from the heights of Gemiancourt sent shot and shell into the devoted squares whenever the French horseman withdrew, they not only repelled their assailants, but Kempt's and Pack's brigades, led, on by Picton, actually advanced against and through their charging foes, and with stern determination made good to the end of the day the ground which they had thus boldly won. Some, however, of the British regiments were during the confusion assailed by the French cavalry before they could form squares, and suffered severely. One regiment, the 92d, was almost wholly destroyed by the cuirassiers. A French private soldier, named Lami, of the 8th regiment of cuirassiers, captured one of the English colours, and presented it to Ney. It was a solitary trophy. The arrival of the English Guards about half- past six o'clock, enabled the Duke to recover the wood of Bossu, which the French had almost entirely won, and the possession of which by them would have enabled Ney to operate destructively upon the allied flank and rear. Not only was the wood of Bossu recovered on the British right, but the inclosures of Pierremont were also carried on the left. When night set in the French had been driven back on all points towards Frasne; but they still held the farm of Gemiancourt in front of the Duke's centre. Wellington and Muffling were unacquainted with the result of the collateral battle between Blucher and Napoleon, the cannonading of which had been distinctly audible at Quatre Bras throughout the afternoon and evening. The Duke observed to Muffling, that of course the two Allied armies would assume the offensive against the enemy on the morrow; and consequently, it would be better to capture the farm at once, instead of waiting till next morning. Muffling agreed in the Duke's views and Gemiancourt was forthwith attacked by the English and captured with little loss to its assailants. [Muffling, p. 242.]