At dawn on 15 June 1815, Napoleon’s 135,000 man army began their march on Belgium, specifically to isolate and destroy both the Duke of Wellington’s Anglo-Dutch-German Army, and Field Marshal Gerhard Von Blucher’s Prussian Army.

Both Allied armies were spread out below Brussels so they could more easily procure supplies from the local population and cover the many avenues of advance Napoleon could take into the country. However, Napoleon’s sudden advance went completely unnoticed. It would be six hours before the first Prussian cavalry reported the French movement; and most of Ney’s wing, whom marched on the British, had escaped observation altogether. It would be 3 pm before the first of Blucher’s couriers reached Wellington with the news. By then he had received his first report from the Prince of Orange that a single Dutch Brigade was in contact with French cavalry and infantry at the vital crossroads of Quatre Bras.

Wellington was left in a dilemma. If Napoleon was attempting to split the Allied armies and defeat them in detail (he was), the crossroads at Quatre Bras was key terrain: any attempt by Blucher to reinforce Wellington or Wellington to march to Blucher must pass through Quatre Bras. A French force there would isolate both Allied armies, even though that French force would be isolated and open to its own destruction. Nevertheless, the capture of Quatrain Bra was the obvious French course of action because it would sacrifice that force for the eventual destruction of both allied armies. However, Napoleon rarely did the obvious, and a French advance on Mons would be disastrous for Wellington because it would cut him off from the sea and his supplies. To Wellington, the French at Quatre Bras still might be a feint (It wasn’t, Wellington just overthought it like the Sicilian in the Princess Bride).

Nonetheless, increasingly desperate messages arrived from the Prince of Orange whom was convinced 320,000 French troops were opposite him (it was actually 33,000). At 4 pm, Wellington realized the magnitude of the impending disaster and said, “Napoleon has humbugged me, by God; he has gained twenty-four hours’ march on me!” By 6 pm, he had the initial orders written for much of his army to concentrate on Quatre Bras the next day. But he didn’t send them.

On the evening of 15 June 1815, Wellington and his senior officers were attending a ball in Brussels. The ball, hosted by Charlotte, the Duchess of Richmond, promised to be the gala event of the year. The who’s who of Dutch and Belgian society were in attendance. A flurry of horsemen galloping desperately from the estate were sure to be seen by the guests. Wellington’s Anglo-Allied Army in the Netherlands required Dutch and Belgian civic stability and cooperation. A sizeable portion of his army was Dutch, and he required the support of the Dutch population for recruits and replacements. Their support kept provision prices down, which lessened the burden on the Royal Navy, and precluded foraging. The majority of his troops were British, German, and Indian, and Dutch goodwill was required to smooth over “cultural misunderstandings.” Wellington was further dependent on his hosts for information to monitor the precarious political situation and wage the undeclared war against French leaning subversives, many of whom were in attendance. Wellington wanted to portray that all was in order and taken care. Spooking the most important Belgian and Dutch civilian influencers in the two countries, even for a seemingly good reason such as a French invasion, would do him no good. In any case, the riders probably wouldn’t find Wellington’s subordinates: they were all assuredly on the road to the ball themselves.

Wellington was already late for the dinner portion and if he did not show soon, panic would inevitably take hold of the guests, especially once they learned that Napoleon had crossed the Sambre River and was engaged with their champion, the Prince of Orange. For the next five hours, between the toasts and dances with the crème of Belgian and Dutch society, Wellington issued his orders to his commanders. He would fight Napoleon at Quatra Bras in order to maintain contact with the Prussians at Ligny, and if either Allied army faltered, Wellington would fall back to a low ridge south of the Belgian town of Mont St Jean, where he and his staff had spent an enjoyable afternoon the year before. Contact with the Prussians must be maintained at all costs, lest Napoleon destroy them in detail. Wellington was under no illusion that he could defeat Napoleon by himself, he needed Blucher and his Prussians.

Wellington’s subordinates’ aides raced back to their units to prepare for battle the next day, while the senior officers continued to dance and drink as if nothing was amiss, much to the delight of the British, Belgian, and Dutch ladies. Around 1 am on 16 June 1815, Wellington locked himself in a backroom with his corps and division commanders, and with a borrowed map, confirmed his orders, ensured his commanders understood his intent, and worked through a short map rehearsal.

As rumors began to make their way into the ball of Napoleon’s invasion, tearful goodbyes replaced merrymaking, but by that point Wellington had achieved his desired effect. At 2 am, on the morning of the inevitable showdown with Napoleon, Wellington and his men emerged from the room. He took his leave from the Duchess of Richmond, while his staff and subordinates said farewell to the remaining guests. Once off the estate, Wellington, his staff, and his commanders raced back to their headquarters.

The Duchess of Richmond’s Ball was the most famous, and no doubt enjoyable, orders group in history.

Many officers rode into battle still wearing the finery in which they attended the ball. Eleven of the Duchess’ of Richmond invited guests would be dead in the next few days, and many more wounded.