Waterloo 1815: What Actually Decided the Battle?

What decided Waterloo?

Ask the question in different countries and different answers appear. Wellington chose the right ground. British infantry squares broke the French cavalry. Ney wasted the cavalry. Napoleon started too late. Hougoumont consumed the French. La Haye Sainte fell too late. The Imperial Guard failed. Blücher arrived and won it. Grouchy failed to arrive and lost it.

Every one of those statements touches something real. None explains the battle on its own.

Waterloo on 18 June 1815 was the closing battle of a four-day campaign in which Napoleon had tried to separate Wellington's Anglo-Allied army from Blücher's Prussians. By the time the armies faced one another at Mont St Jean, that strategic aim had failed in one crucial respect: the Prussians had survived Ligny, regrouped around Wavre and remained committed to supporting Wellington.

The battlefield problem was therefore simple to state and difficult to solve: could Napoleon break Wellington before enough Prussians arrived to turn a frontal battle into a two-army coalition battle?

Waterloo has too many sources, not too few

The battle is exceptionally well documented and unusually difficult to narrate cleanly because the surviving evidence comes from different national and institutional traditions.

• Wellington's dispatch, published in the London Gazette only days after the battle, is indispensable but is still the official report of the victorious commander.
• Prussian reports and histories are essential for the march from Wavre and the fighting around Plancenoit, areas long given less space in English-language retellings.
• French memoirs contain valuable tactical detail but were often written after defeat, when responsibility for Ney, Grouchy, staff officers and Napoleon himself had become politically charged.
• Later national histories inherited different source families and emphases.
• Modern archaeology, including work by Waterloo Uncovered, can test where fighting happened and how intensively, although material evidence cannot by itself tell us what a commander intended.

A famous anecdote repeated in ten later books may still descend from one memoir. Waterloo rewards source comparison more than source counting.

The campaign had already shaped the battle

Napoleon crossed the Sambre on 15 June and drove between the coalition armies. On 16 June he defeated the Prussians at Ligny while Ney fought Wellington at Quatre Bras. The French had gained the central position but had not destroyed either enemy army.

Blücher withdrew towards Wavre rather than eastward away from Wellington. Wellington then retired to Mont St Jean on 17 June. Blücher promised support.

That promise is the strategic foundation of Waterloo. Wellington was not intending to hold one ridge against Napoleon indefinitely. He was buying time for coalition concentration.

For the campaign-level story, read Hundred Days 1815: Was Waterloo Inevitable?.

Mont St Jean was strong ground, not magic ground

Wellington's main line occupied a ridge across the Brussels road. The reverse slope screened many troops from direct French observation and some artillery fire. Forward positions — especially Hougoumont and La Haye Sainte — forced the French to fight for important ground before they could exploit the ridge itself.

The position also had vulnerabilities. La Haye Sainte stood dangerously close to the centre. The eastern approaches mattered because that was where Prussian columns would appear. If the French captured the strongpoints early and forced a rupture before coalition support arrived, the ridge alone would not save the army.

Did Napoleon simply start too late?

Heavy rain fell before the battle. The familiar explanation says Napoleon waited for the ground to dry enough for artillery.

The wet ground mattered. Artillery movement and cavalry manoeuvre were harder in mud, and roundshot behaved differently in soft soil. But the claim that Napoleon merely sat waiting for sunshine and thereby lost the battle turns a morning of reconnaissance, deployment and preparation into one neat mistake.

Even the exact opening time varies across accounts. The safest conclusion is that wet ground contributed to delay and reduced some French advantages. It was a factor, not a sufficient explanation for defeat.

Hougoumont: a local fight with strategic consequences

Fighting around Hougoumont began on Wellington's right and continued for most of the day. French troops briefly penetrated the north gate, but the defenders closed it and retained the complex.

Later narratives often claim Napoleon intended Hougoumont merely as a diversion and that subordinates foolishly fed troops into it. The effect is clearer than the original intention: substantial French effort became tied to a position that never fell.

Battlefield attacks evolve. An action conceived on a limited scale can become important because resistance, reinforcement and opportunity change the local situation. Modern archaeology at Hougoumont has helped test the physical landscape and intensity of the fighting without solving every command question.

d'Erlon's attack and the heavy cavalry counterstroke

French artillery prepared the attack on Wellington's left-centre before d'Erlon's I Corps advanced uphill. The assault created a serious crisis but was met by Allied infantry and then a dramatic heavy-cavalry counterattack.

British cavalry helped break the immediate French attack and captured eagle standards. Parts of it then pursued too far, lost cohesion and were counterattacked themselves.

That episode is a useful warning against branch mythology. Cavalry did not simply “save the line”. Its success depended on timing, infantry resistance, terrain and the French formation already being under stress.

The Prussians changed Napoleon's choices before they changed the front line

By mid-afternoon Napoleon had credible evidence that Prussian formations were approaching his right. Bülow's IV Corps was the leading major formation, with additional Prussian corps following from Wavre.

This mattered before every Prussian soldier entered combat. Napoleon now had to allocate troops towards the eastern flank and later to Plancenoit. Reserves that might otherwise have supported the main attack on Wellington acquired a second mission.

Blücher's intervention was therefore not a theatrical arrival in the final minutes. Prussian movement progressively altered the French command problem.

This does not reduce Wellington's army to men waiting for rescue. Wellington's resistance and Blücher's march were mutually dependent parts of the same coalition victory.

Ney's cavalry attacks and the problem of post-war blame

The repeated French cavalry attacks against Allied squares are among the most familiar scenes of Waterloo. A common explanation says Ney saw movement behind the ridge, mistook it for retreat and committed the cavalry prematurely.

The broad idea is plausible, but the exact sequence of authorisation, reinforcement and Napoleon's knowledge remains debated. The commitment grew over time, and post-war blame naturally concentrated on Ney because so much mounted strength was consumed without breaking the Allied centre.

The tactical problem is clearer. Infantry squares were extremely difficult for unsupported cavalry to break while cohesion held. Cavalry could force infantry into static formations and expose them to artillery, but decisive success usually required close coordination with other arms. At Waterloo that coordination never produced the required collapse.

For the formation itself, see How Infantry Squares Stopped Cavalry.

La Haye Sainte created the opening Napoleon needed

French troops eventually captured La Haye Sainte after its defenders had been worn down and ammunition became critically short. Its fall opened dangerous ground close to Wellington's centre and allowed French firepower to operate at shorter range.

This was one of the moments when Allied defeat was genuinely possible.

But by then Napoleon was also fighting the Prussians around Plancenoit. The battle had become a resource-allocation crisis. The French had gained an important central strongpoint at almost the same stage that their eastern flank demanded more troops.

Saying La Haye Sainte fell “too late” therefore makes sense only if time is understood strategically: coalition convergence had changed the value of every remaining minute.

The Imperial Guard and the collapse of confidence

In the evening Napoleon committed elements of the Imperial Guard against Wellington's line. The attack failed. Seeing Guard formations recoil contributed to the collapse of French confidence while Prussian pressure intensified.

Popular memory compresses this into one monolithic Guard assault and attaches famous last words to it. The actual commitment involved different formations and a sequence reconstructed differently by witnesses.

The secure point is simpler. Napoleon's final elite reserve failed to create a breakthrough at the moment the coalition pressure was becoming overwhelming. Once the French army began to retreat, the Allied and Prussian advance turned defeat into rout.

What Wellington's dispatch can — and cannot — tell us

Wellington's dispatch was published in the London Gazette on 22 June 1815. It records repeated French attacks, Allied losses and distinguished officers and remains one of the most important contemporary routes into the battle.

Official dispatches are selective by nature. They explain victory to government and public. Historians have long argued over how fully Wellington represented Prussian intervention and some of his own campaign decisions.

The sensible approach is neither to treat the dispatch as a complete transcript nor to discard it. It has to be read beside Prussian material, French records and the physical evidence.

What archaeology adds

Waterloo Uncovered has excavated and surveyed areas including Hougoumont, Mont-Saint-Jean and ground around La Haye Sainte. Finds include musket balls, artillery-related material, uniform objects and human remains associated with the battle and its aftermath.

Projectile distributions and structural evidence can help test the intensity of fighting in contested spaces. But the battlefield has been cleared, farmed, memorialised and altered for more than two centuries. The Lion's Mound and later roads changed parts of the landscape. Absence of an artefact is not automatically evidence that combat did not occur there.

Casualties: scale is safer than false precision

All major totals are estimates assembled from returns, missing men, prisoners and later reconciliation. Wellington's own dispatch described his losses as immense. Modern summaries commonly put combined Allied and Prussian losses in the tens of thousands and French losses higher once prisoners and the rout are included.

The precise number varies with definitions. The important point is the scale: Waterloo was a very costly coalition victory and a catastrophic French operational defeat.

So what actually decided Waterloo?

Claim	Assessment
Wellington's ridge alone won the battle	False single-cause explanation
Wet ground materially affected the French opening	Strongly supported
Waiting for the mud to dry was the one mistake that lost Waterloo	Over-simplified
Hougoumont tied down French resources	Strongly supported
Ney alone launched every cavalry attack through one obvious blunder	Contested and over-compressed
La Haye Sainte created a serious late crisis	Strongly supported
The Prussian arrival was merely an end-of-battle footnote	False
The Imperial Guard's repulse mattered tactically and psychologically	Strongly supported
Waterloo was fundamentally a coalition victory	Very high confidence

The strongest single explanation is not a unit or a dramatic moment. Waterloo was decided by the French failure to break Wellington before coalition concentration transformed the battle.

Wellington's army had to survive. Blücher's army had to arrive. French attacks had to fail often enough and long enough for those two facts to meet on the same field.

Evidence that could refine the picture

Securely dated French staff orders could materially alter the reconstruction of who authorised the large cavalry commitments and when. Independent contemporary timing evidence could sharpen the sequence of the Guard attack and Prussian arrival. Archaeological concentrations around La Haye Sainte, Hougoumont or artillery positions could refine our understanding of local fire and movement.

Any interpretation claiming that one national contingent “really won” Waterloo should be tested against the same counterfactual: remove Wellington's prolonged resistance or remove Blücher's intervention. In either case the coalition plan ceases to function as it did historically.

Primary routes and further reading

• The Gazette — Wellington's Waterloo dispatch — contemporary official report published 22 June 1815.
• National Army Museum — Battle of Waterloo — modern institutional overview and force context.
• National Army Museum — Hundred Days Campaign — operational setting.
• Fondation Napoléon — Blücher and the Waterloo Campaign — Prussian-centred chronology and march from Wavre.
• Waterloo Uncovered — Archaeology — modern excavation, survey and material evidence from the battlefield.

Related Regimental Record investigations

• Hundred Days 1815: Was Waterloo Inevitable?
• How Infantry Squares Stopped Cavalry
• Trafalgar 1805: Nelson, the Line and the Battle That Secured the Seas
• Command biographies: Napoleon · Wellington · Blücher · Ney

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From the collection

Explore the complete Waterloo 1815 collection. For the infantry formation at the centre of the cavalry debate, see the Waterloo 1815 Infantry Line T-Shirt.