Any opportunity that Napoleon might have had to attack Wellington as he was withdrawing from Quatre Bras after ten o’clock on the morning of the seventeenth was passed up by him and Ney, and when Napoleon rejoined Ney there he shouted: ‘You have ruined France!’ With the rain making the transport of artillery tough going, the French army followed Wellington up the Charleroi-Brussels road, hoping for the opportunity of a decisive encounter before the Prussians — of whose exact whereabouts Napoleon (and indeed Grouchy) was uncertain — could regroup. It all came down to numbers and odds: Napoleon had a larger army than either Wellington or Blücher, but not larger than both of them combined.
The French followed hard on the heels of the withdrawing British, and a compelling narrative of the day was given by Captain Cavalié Mercer of the British horse artillery, whose memoirs of the campaign are a superb historical source. ‘We galloped for our lives through the storm, straining to gain the enclosures about the houses of the hamlets,’ wrote Mercer. ‘Lord Uxbridge urging us on, crying, “Make haste! — Make haste! For God’s sake gallop, or you will be taken!”’ The thunderstorms that were developing — ‘Flash succeeded flash, and the peals of thunder were long and tremendous’— put paid to French hopes of catching up with the Anglo-Allied rearguard, although there was an occasion at Genappe where the British Life Guards had to charge French lancers to cover the withdrawal, which they did successfully, ‘sending their opponents flying in all directions’. There were a series of narrow escapes for the Anglo-Allied army retreating from Quatre Bras, which Mercer described as ‘a fox hunt’.
The torrential downpour of 17 June continued until long after the Anglo-Allied rearguard had halted on the slopes of Mont St Jean, a few miles south of Waterloo. Those soldiers who did not have tents slept in their greatcoats, soaking wet. A British infantry private (later sergeant) named William Wheeler of the 51st Regiment recalled how ‘We sat on our knapsacks until daylight without fires. The water ran in streams from the cuffs of our jackets, in short we were wet as if we were plunged overhead in a river. We had one consolation, we knew the enemy [was] in the same plight. The morning of the 18th June broke upon us and found us drenched with rain, benumbed and shaking with cold.’An officer later wrote that it seemed as if the water was being tumbled out of heaven in tubs.13
Charles O’Neil, a private in the 28th Regiment of Foot who had survived the terrible storming of Badajoz in the Peninsular War, recorded his memories of the night before the battle. A thief, deserter, fugitive and conman, O’Neil was not much given to sentimentality, but his account of the emotions of the night rings profoundly true:
I was just endeavouring to compose myself to sleep when my comrade spoke to me, saying that it was deeply impressed on his mind that he should not survive the morrow; and that he wished to make an arrangement with me, that if he should die and I should survive, I should inform his friends of the circumstances of his death, and that he would do the same for me, in case he should be the survivor. We then exchanged the last letters we had received from home, so that each should have the address of the other’s parents. I endeavoured to conceal my own feelings, and cheer his, by reminding him that it was far better to die on the field of glory than from fear; but he turned away from me, and with a burst of tears, that spoke the deep feelings of his heart, he said, ‘My mother!’ The familiar sound of this precious name, and the sight of his sorrow, completely overcame my attempts at concealment, and we wept together.14
(Sure enough, although O’Neil himself was wounded at Waterloo, his comrade was killed twenty-five minutes into the action, and O’Neil duly informed the parents of the circumstances.)
Before daybreak, Wellington received a message that would make the gruelling night undergone by the British army wholly worthwhile. Blücher sent word that as soon as it was light enough to march, he would be sending not only Bülow’s corps (which had not taken part in Ligny) to Wellington’s aid, but two whole corps — virtually the entire Prussian army — leaving only one corps to guard Wavre against Grouchy coming up from Gembloux. This was about treble the numbers Wellington had been expecting and hoping for, and it completely altered his thinking about the battle that was clearly to be joined the next day.
Instead of merely a holding action in front of the large Forest of Soignes to his rear, through which there was only one road to Brussels, Wellington could now envisage doing to Napoleon what Napoleon had hoped to do to the Prussians at Ligny: crush the enemy with a surprise eruption of extra troops onto its flank in the course of the battle.
For Napoleon had not the first hint of a suspicion that the Prussians, largely through the superhuman efforts of their commander, had been transformed in less than forty-eight hours from a defeated force fleeing the battlefield of Ligny into a disciplined army ready to take the offensive against the French once again. Meanwhile Grouchy, despite the large force at his disposal, had failed to make significant contact with the Prussian rearguard. He had also taken seven hours to march the six miles to Gembloux, which even in the torrential rain was a tortoise-like speed.
Napoleon desperately needed that force to be commanded by a marshal of dash and verve, but instead he had given the job to Grouchy. The most impressive cavalry commander in Europe, Napoleon’s brother-in-law Joachim Murat, King of Naples, had fled Italy and offered his services, but the Emperor had turned him down. Marshal Davout was holding down the job of minister of war back in Paris, while Marshal Suchet was commanding the divisions guarding France’s eastern approaches. Most of the other twenty-six marshals were either dead, had declared for the Bourbons, or were refusing to commit themselves to either side.
The knowledge that his left flank would be protected by the Prussians encouraged Wellington to strengthen the right and centre of his line. He also left over 17,000 men (3,000 British and 14,000 Dutch and Hanoverian) off the battlefield altogether, stationing them nine miles to the west at a village named Hal, under the joint commands of Prince Frederick of the Netherlands and Lieutenant-General Sir Charles Colville, who were both under the overall command of General Lord Hill. These troops would, Wellington hoped, be able to prevent any extravagant outflanking movement on the right flank, since he suspected that Napoleon might only be feinting at the Charleroi—Brussels road and really intended to march on Brussels via Mons.
Many historians — and not only historians: Napoleon himself fastened upon it — have criticised Wellington for leaving so large a force a two-or three-hour march away from the battlefield and for not recalling them the moment it became clear that Napoleon intended no large-scale manoeuvre but only a ‘hard pounding’ attack up the centre. They have even likened Wellington’s detachment at Hal to Napoleon sending off Marshal Grouchy, thereby deliberately absenting a large body of men who could have been invaluable at the battle. In Wellington’s defence the historian Jac Weller has argued that: