How Napoleon dismantled the legendary Prussian army in just five weeks of warfare

History · Published 29 September 2026 Swipe more like this →

In short: In the autumn of 1806, Napoleon Bonaparte shattered the myth of Prussian military invincibility. In a lightning campaign lasting only five weeks, he crushed the forces of Frederick William III, fundamentally redrawing the map of Europe and reducing the Prussian state to half its former size by July 1807.

The conflict began as Prussia, emboldened by a secret alliance with Russia signed in July 1806, sought to threaten Napoleon’s communication lines. Under the command of Charles William Ferdinand, the Duke of Brunswick, the Prussian-Saxon army moved slowly westward. Napoleon responded with characteristic speed, marching northward through the Thuringian Forest to sever their connection to the Elbe River and force a decisive engagement before Russian reinforcements could arrive.

On October 14, 1806, the campaign culminated in two simultaneous battles. At Jena, Napoleon engaged Prince Friedrich Ludwig of Hohenlohe-Ingelfingen with 54,000 troops, sweeping his 38,000-strong force and their reinforcements from the field by mid-afternoon. Simultaneously, 13 miles to the north at Auerstädt, Louis-Nicolas Davout’s secondary force of 26,000 men faced the main Prussian army. Despite being vastly outnumbered, Davout held his ground for six hours. When the Duke of Brunswick was mortally wounded, the Prussian command faltered, and news of the defeat at Jena caused their remaining resistance to collapse.

The consequences were catastrophic for Prussia. The double victory cost the French roughly 12,000 casualties, while the Prussians and Saxons suffered 24,000 casualties and 20,000 captures. By the Treaty of Tilsit in July 1807, Prussia was halved in size. The engagement proved that the outdated military system inherited from Frederick II the Great was no match for Napoleon’s tactical agility. Davout, for his extraordinary stand at Auerstädt, was later honored as the Duke d’Auerstädt, cementing his role in one of the most decisive military campaigns of the era.

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