Meanwhile the French and the Prussians had been fighting in and round the villages of Ligny, Sombref, and St. Armand, from three in the afternoon to nine in the evening, with a savage inveteracy almost unparalleled in modern warfare. Blucher had in the field, when he began the battle, 83,417 men, and 224 guns. Bulow's corps, which was 25,000 strong, had not joined him; but the Field-Marshal hoped to be reinforced by it, or by the English army before the end of the action. But Bulow, through some error in the transmission of orders, was far in the rear; and the Duke of Wellington was engaged, as we have seen, with Marshal Ney. Blucher received early warning from Baron Muffling that the Duke could not come to his assistance; but, as Muffling observes, Wellington rendered the Prussians the great service of occupying more than 40,000 of the enemy, who otherwise would have crushed Blucher's right flank. For, not only did the conflict at Quatre Bras detain the French troops which actually took part in it, but d'Erlon received orders from Ney to join him, which hindered d'Erlon from giving effectual aid to Napoleon. Indeed, the whole of d'Erlon's corps, in consequence of conflicting directions from Ney and the Emperor, marched and countermarched, during the 16th, between Quatre Bras and Ligny without firing a shot in either battle.

Blucher had, in fact, a superiority of more than 12,000 in number over the French army that attacked him at Ligny. The numerical difference was even greater at the beginning of the battle, as Lobau's corps did not come up from Charleroi till eight o'clock. After five hours and a half of desperate and long-doubtful struggle, Napoleon succeeded in breaking the centre of the Prussian line at Ligny, and in forcing his obstinate antagonists off the field of battle. The issue was attributable to his skill, and not to any want of spirit or resolution on the part of the Prussian troops; nor did they, though defeated, abate one jot in discipline, heart, or hope. As Blucher observed, it was a battle in which his army lost the day but not its honour. The Prussians retreated during the night of the 16th, and the early part of the 17th, with perfect regularity and steadiness, The retreat was directed not towards Maestricht, where their principal depots were established, but towards Wavre, so as to be able to maintain their communication with Wellington's army, and still follow out the original plan of the campaign. The heroism with which the Prussians endured and repaired their defeat at Ligny, is more glorious than many victories.

The messenger who was sent to inform Wellington of the retreat of the Prussian army, was shot on the way; and it was not until the morning of the 17th that the Allies, at Quatre Bras, knew the result of the battle of Ligny. The Duke was ready at daybreak to take the offensive against the enemy with vigour, his whole army being by that time fully assembled. But on learning that Blucher had been defeated, a different course of action was clearly necessary. It was obvious that Napoleon's main army would now be directed against Wellington, and a retreat was inevitable. On ascertaining that the Prussian army had retired upon Wavre, that there was no hot pursuit of them by the French, and that Bulow's corps had taken no part in the action at Ligny, the Duke resolved to march his army back towards Brussels, still intending to cover that city, and to halt at a point in a line with Wavre, and there restore his communication with Blucher. An officer from Blucher's army reached the Duke about nine o'clock, from whom he learned the effective strength that Blucher still possessed, and how little discouraged his ally was by the yesterday's battle. Wellington sent word to the Prussian commander that he would halt in the position of Mont St. Jean, and accept a general battle with the French, if Blucher would pledge himself to come to his assistance with a single corps of 25,000 men. This was readily promised; and after allowing his men ample time for rest and refreshment, Wellington retired over about half the space between Quatre Bras and Brussels. He was pursued, but little molested, by the main French army, which about noon of the 17th moved laterally from Ligny, and joined Ney's forces, which had advanced through Quatre Bras when the British abandoned that position. The Earl of Uxbridge, with the British cavalry, covered the retreat of the Duke's army, with great skill and gallantry; and a heavy thunderstorm, with torrents of rain, impeded the operations of the French pursuing squadrons. The Duke still expected that the French would endeavour to turn his right, and march upon Brussels by the high road that leads through Mons and Hal. In order to counteract this anticipated manoeuvre, he stationed a force of 18,000 men, under Prince Frederick of the Netherlands, at Hal, with orders to maintain himself there if attacked, as long as possible. The Duke halted with the rest of his army at the position near Mont St. Jean, which, from a village in its neighbourhood, has received the ever-memorable name of the field of Waterloo.