"Victory belongs to the most persevering"
(Attributed to Napoleon Bonaparte)
The Battle of Jena (Iéna):
Napoleon Bonaparte, his plans to invade the island of Britain in 1805 thwarted by diplomatic proceedings and the Battle of Trafalgar, had turned to the east of Europe to face the combined forces of Russia and Austria. This third anti-French alliance, organised by Great Britain to fight Napoleon, had been effectively destroyed at Austerlitz in the December of 1805. Prussia, however, was becoming increasingly belligerent and decided to join the allies just before the battle of Austerlitz took place. The Prussians had formed an ultimatum to be put to the Emperor of France, one that would certainly and deliberately deteriorate relations between the two nations in order to provoke war.
Napoleon did not read the ultimatum until after his victory at Austerlitz, although it arrived to him several days beforehand. Once he had read it, however, the emperor took his revenge on Prussia by enforcing terms that the Germans were forced to accept, having no army mobilised at that time. France therefore gained the territories of Cleves, Ansbach and Neuchatel. The newly formed Confederation of the Rhine also threatened Prussian influence in the area, a humiliating blow. When Napoleon offered Hanover to Britain in return for an end to the hostilities in 1806, despite the fact that it was already promised to Prussia, Prussia (or more accurately her monarch, Queen Louise) would take no more. The Prussian army mobilised on the 10th of August and occupied the province of Saxony (Sachsen). Saxony took Prussia's side once it became clear that she could not remain neutral.
So, by the autumn of 1806, war between France and Prussia was imminent. Napoleon again moved swiftly, as prior to Austerlitz, and his strategy was to keep Prussia isolated from her two allies (Saxony and Russia). To do this he planned to strike deep into German territory, towards Dresden and Berlin. This would also keep French forces close enough to the Austrian border to keep Austrian forces quiet (although after Austerlitz it was unlikely that they would play a significant role in the future campaign).
The Prussians, meanwhile, were slow in formulating a plan. Despite being well trained in contemporary tactics, the army lacked a leader in the same league as the French commander. Napoleon had succeeded in advancing so that the Prussians actually had to turn and face the threat to their rear, as they too had moved forward in an attempt to cut Napoleon's lines of communication but had been out-maneouvred. It was only by the 5th of October, after weeks of procrastination, that this was discovered. Prince Louis Ferdinand was killed in a skirmish between his forces and the French Corps commanded by Lannes at Saalfeld. By the 13th of October 1806, Lannes found himself facing what appeared to be the entire Prussian army near the town of Jena. Napoleon, who had expected to fight three days later than this at Erfurt, rushed his forces towards this position, whilst sending troops under Marshal Davout to block the Prussian's route of retreat. Napoleon had 25, 000 men ready to fight by the early hours of the 14th, against 40, 000 Prussians (commanded by Prince Hohenlohe). The French, however, could expect up to 55, 000 more troops by noon as the rest of the army caught up. The main Prussian army of over 60, 000, under the Duke of Brunswick, was also on its way, but would come across Davout and his 30, 000 at Auerstädt before the day was over.
The action at Jena on the 14th of October 1806 took place on a ridge (the "Landgrafenberg") northwest of the town. The villages of Closewitz, Lutzeroda, Cospeda and Vierzehnheiligen also lay on the battlefield. The initial moves, made by the French around 6.30 am, were centred around these villages.
It was Lannes who made the first attack, ordered by Napoleon to win more space for the French on the ridge. Lannes' V Corps and Soult's IV Corps (on the right of the French line) engaged the Prussians in a firefight between their respective infantries. Soult's men repelled an attempted Prussian attack on their side of the battle. Meanwhile, the French VII Corps (led by Marshal Augereau) was advancing around the Prussian right flank along the Jena-Weimar road, hidden from view in a valley.
At this moment (around 9.30 am) Marshal Ney arrived with an advance guard of 3, 000 men. Ney led his two squadrons of cavalry and two battalions of infantry towards Vierzehnheiligen, to the left of Lannes. This unauthorised attack was disastrous, as these Frenchmen were soon cut off. Hohenlohe had ordered an attack with 45 squadrons of cavalry and 11 infantry battalions, and threatened to overrun Ney's overextended troops. Napoleon realised Ney's precarious position, and sent Lannes' Corps to attack, in order to link up with Ney, whilst cavalry attacked the Prussians directly. Augereau, meanwhile, covered Ney's left flank. The survivors of Ney's rash assault were relieved by Lannes around Vierzehnheiligen, and Napoleon's prized artillery pounded the floundering Prussians, who stayed out in the open due to Hohenlohe's belief that 15, 000 men were on their way to him, inflicting heavy casualties.
At around 12.30 pm, an hour after the artillery barrage had begun, Napoleon won the battle. Marshals Soult and Augereau would pin down each Prussian flank, whilst Lannes and Ney (now with his entire Corps) would attack and breach the Prussian center. The French repeatedly attacked the enemy line, and artillery was brought forward to wither the enemy line with canister. The two Corps on the flanks also succeeded in driving the Prussians back. No reinforcements seemed to be forthcoming for Hohenlohe, and he realised that soon his flanks would be turned and his entire force destroyed. The Prussian commander therefore ordered a general retreat.
Napoleon then, at 1.45 pm, unleashed Murat and his heavy cavalry. Coming down on the retreating enemy like a storm, the orderly retreat turned into a rout. It was only the brave move of one battalion and the remnants of a Prussian division, forming square on the road to buy the rest of their forces some time, that prevented a real massacre. The nain battle was over bu 2.30pm.
Hohenlohe made another mistake, however. In coming across the 15, 000 men he had been waiting for during the retreat, the Prussian commander ordered them not to form a protective rearguard, but to attack the French. These 15, 000, led by Ruchel, succeeded in stopping Lannes but soon found themselves outflanked, and so fell back. Prussian cavalry, trying to cover the retreat, were scattered by artillery, and Murat's horsemen again attacked the retreating line. The Prussian soldiers again fled against the onslaught, bringing an end to the battle.
This battle destroyed the myth of Prussian invincibility created by Frederick the Great and further showed that France dominated mainland Europe. The French lost 5, 000 men at Jena, killed or wounded. The Prussians in comparison lost 10, 000 dead, 15, 000 wounded, 34 of their regimental colours and 120 artillery pieces.
The French success at Jena also influenced the result of the battle at Auerstädt, which was taking place 8 miles to the north, completely unknown to Napoleon. News of their defeat at Jena demoralised the Prussian troops there, facilitating the amazing French victory at this battle too. After these comprehensive defeats, the Prussian forces were left scattered across the country, and the remainder of the campaign for the French was a mopping up operation (conducted by Marshal Bernadotte, whose Corps had participated in neither battle).
Interestingly, the double disaster of Jena and Auerstädt also led to the complete re-organisation of the Prussian army, which laid the foundations for its success later that century (for example at Sadowa (Königgrätz) in 1866 and in the Franco-Prussian War of 1870-1). This resurgence was evident as early as the 1810s, and was greatly facilitated by the wave of German nationalism at this time. This directly led to the unification process led by Bismarck in the mid-1800s, and then on to Wilhelm II and the events of the 20th century.
French forces entered Berlin on the 27th of October, 1806. Almost the whole of Prussia now lay in French hands, and once again the armies sent against France had failed. The Treaty of Tilsit, signed in July 1807, reduced Prussia to half its former size. However, a small number of Prussians in the east still resisted, and Great Britain continued to fund and support the anti-French coalition. The Russians were still willing to fight, and moved towards the Prussian border to meet up with those that remained defiant. Napoleon would have to fight again, this time in the cold Russian winter. French forces were also preparing to move into Spain in the west the next year. It would be these two actions, the invasions of Russia and Spain, that would turn the course of the Napoleonic Wars against Napoleon Bonaparte and France, leading to Leipzig and ultimately Waterloo.
"Jena 1806: Napoleon Destroys Prussia", by D. Chandler (published 1993)
"The Jena Campaign 1806", by F.N. Maude (first published 1909, 1998 edition)