War of the Fourth Coalition

The Battle of Auerstädt was fought on 14 October 1806 on the plateau west of the river Saale, in present-day Thuringia, as one of the twin engagements alongside Jena that opened the War of the Fourth Coalition. Together, the two battles inflicted a catastrophic defeat on the Prussian Army, an institution that had undergone little reform in roughly half a century. The scale of the disaster was decisive at the strategic level: Prussia was effectively subjugated to the French Empire as a result, and did not re-emerge as an active coalition partner against Napoleon until the formation of the Sixth Coalition in 1813. The engagement thus removed one of the major continental powers from the war at its outset, fundamentally altering the balance of the conflict for the following seven years.

The Battle of Czarnowo secured a French crossing of the Wkra River during the winter operations of the War of the Fourth Coalition. Davout's III Corps forced the passage at the river's mouth and drove eastward to the village of Czarnowo, compelling Ostermann-Tolstoy to withdraw his Russian forces to the east after an all-night engagement. The action extended French operational reach north-northwest of Warsaw along the Narew, maintaining pressure on Russian positions as the campaign continued into early 1807. Casualties on both sides were roughly equal despite the disparity in engaged strength, indicating the difficulty of the night river assault.

At Halle on 17 October 1806, Bernadotte's corps defeated the Prussian Reserve under the Duke of Württemberg, inflicting roughly 5,000 casualties and forcing the surviving Prussians to retreat northeast toward Dessau. The engagement formed part of the broader French offensive during the War of the Fourth Coalition, occurring in the same operational window as the twin disasters at Jena and Auerstedt. By breaking and scattering the Prussian Reserve, the battle denied Prussia a coherent force that might otherwise have screened or covered the retreat of other Prussian formations. The direction of the Prussian withdrawal toward Dessau, away from the main body of the army, further fragmented Prussian resistance and contributed to the rapid collapse of organized opposition in central Germany during the campaign.

The Battle of Lübeck was a direct consequence of the Prussian collapse at Jena–Auerstedt, with Blücher's retreating force of roughly 17,000 men pursued north to the neutral Baltic port city by three French marshals commanding between 30,000 and 35,000 troops. The French inflicted a severe defeat, driving the Prussians from Lübeck and producing Prussian casualties estimated between 6,000 and 9,000 against French losses of 1,500–2,000. The action effectively destroyed one of the last organized Prussian field forces still operational after the October disasters, accelerating the collapse of Prussian resistance in the opening phase of the War of the Fourth Coalition. That the battle was fought inside a neutral city underscored the degree to which the French pursuit was conducted without regard for political boundaries, a pattern consistent with Napoleon's operational tempo throughout the 1806 campaign.

The capitulation at Prenzlau on 28 October 1806 effectively eliminated a Prussian corps of 10,000–12,000 men during the broader collapse of Prussian resistance following the twin defeats at Jena-Auerstedt. Murat's cavalry interception of Hohenlohe's retreating force north of Berlin, resulting in the surrender of the entire corps after limited fighting, illustrated how thoroughly French mobile forces were able to pursue and neutralize organized Prussian formations. The loss of some 3,500 casualties and the capitulation of the remainder accelerated the disintegration of the Prussian army as a coherent fighting force in the 1806 campaign, leaving little organized resistance between the French and the Baltic coastline.

The Battle of Pułtusk was fought on 26 December 1806 during the War of the Fourth Coalition, pitting a French force of roughly 25,000–27,000 men under Marshal Jean Lannes against a Russian army of 40,000–45,000 under General Levin von Bennigsen. Despite their numerical superiority and artillery advantage, the Russians absorbed heavy French attacks before withdrawing the following day. Casualties on both sides were substantial and roughly comparable—approximately 3,300 French and 3,500 Russian—leaving the Russian force disorganized for the remainder of the year. The battle denied Bennigsen the ability to exploit his numerical edge and disrupted Russian cohesion at a critical moment in the winter campaign, limiting Russian operational effectiveness in the weeks that followed.

The Battle of Saalfeld was the second engagement of the Prussian Campaign and resulted in a French victory over a combined Prussian-Saxon force. Marshal Jean Lannes's force of roughly 12,800 men defeated Prince Louis Ferdinand's 8,300-strong command, inflicting approximately 1,800 Prussian casualties. The engagement was fought in Thuringia, in the Ernestine duchy of Saxe-Coburg-Saalfeld, placing French forces in a position to continue their advance into Prussia. As an early action in the War of the Fourth Coalition, the outcome at Saalfeld contributed to the sequential pressure France was applying to Prussian forces before the decisive confrontations that would follow later in the campaign.

The Battle of Schleiz on 9 October 1806 was the opening engagement of the War of the Fourth Coalition, marking the first armed contact between Napoleon's Grande Armée and the combined Prussian-Saxon forces. As the Grande Armée advanced north through the Franconian Forest, it struck the left wing of the Prussian-Saxon deployment, which was stretched across a long front. This sequential exposure of an overextended allied line at its leftmost point set the operational pattern for the rapid French envelopment that would characterize the wider campaign. With French forces under Drouet engaging a division less than half their strength, the engagement demonstrated the vulnerability of the Prussian-Saxon disposition before the major engagements that followed days later. Schleiz thus served as the opening blow in a campaign that would bring the Coalition to swift collapse.

The Battle of Waren-Nossentin was a rear guard action fought during the War of the Fourth Coalition, occurring in the immediate aftermath of the wider Prussian collapse following Jena-Auerstedt. Facing a French force roughly two to three times their own strength under Marshal Bernadotte, the Prussian contingents under Pletz and Yorck von Wartenburg yielded ground but avoided the destruction or encirclement that French pursuit operations were designed to achieve. By keeping their formations intact, the Prussian commanders preserved a measure of operational coherence at a moment when Prussian resistance across northern Germany was fragmenting rapidly.

Two days after the Prussian army's catastrophic defeat at Jena–Auerstedt, Marshal Murat accepted the surrender of a Prussian force under the Prince of Orange at Erfurt. The capitulation removed between 10,000 and 12,000 Prussian troops from the field without meaningful resistance, a direct consequence of the demoralization that followed Jena–Auerstedt. Coming so rapidly after that decisive engagement, the fall of Erfurt illustrated the extent to which Prussian military cohesion had collapsed: a force numerically capable of contesting the city yielded to a French column rather than prolong the fight. The surrender accelerated French consolidation of central Germany in the opening phase of the Fourth Coalition campaign.

The Capitulation of Pasewalk illustrates the cascading collapse of Prussian military cohesion following the Battle of Jena-Auerstedt. Two weeks of continuous retreat had so thoroughly demoralized Colonel von Hagen's force that 4,200 Prussian soldiers surrendered to only 1,500 French light cavalry — a force less than a third their size. The event occurred 110 kilometers north of Berlin and roughly 40 kilometers west of Stettin, placing French power deep into northeastern Prussia and demonstrating that organized resistance had effectively dissolved across much of the kingdom. Capitulations of this kind, where numerically superior Prussian garrisons and columns yielded to small French detachments, were a defining feature of the weeks following Jena-Auerstedt and collectively stripped Prussia of its field army far faster than combat alone could have achieved.

The Battle of Allenstein, fought during the opening phase of the 1807 campaign, produced a French field victory and enabled pursuit of the Russian army under Bennigsen. Despite this tactical success, the engagement fell short of Napoleon's operational objective: a decisive engagement that could cripple Russian forces and compel a conclusion to the War of the Fourth Coalition. The battle is thus notable less for what it achieved than for what it did not — French forces under Murat and Soult secured the field but could not translate that advantage into the annihilating blow Napoleon required to end the campaign in the east.

At Guttstadt-Deppen, Bennigsen committed the bulk of Russian strength—some 63,000 troops—against Ney's isolated corps of roughly 17,000, pressing the French back along the route southwest toward the Pasłęka River. Despite the severe numerical disparity, Ney's rearguard action contained Russian exploitation and allowed his corps to disengage intact, crossing to the west bank of the Pasłęka by the end of 6 June. The engagement demonstrated the difficulty Bennigsen faced in translating local numerical advantage into decisive results during the closing phase of the Fourth Coalition campaign in eastern Prussia. Coming roughly a week before Friedland, the Russian failure to destroy Ney's corps left French forces in a position to consolidate rather than absorb a crippling blow before that decisive engagement.

The Battle of Heilsberg on 10 June 1807 was a significant but inconclusive engagement during the War of the Fourth Coalition. Murat's French corps attacked Bennigsen's Russian force ahead of schedule, and the French assaults produced no tangible results by nightfall, after which an operational armistice was concluded. Despite holding a numerical disadvantage — French forces numbered between 50,000 and 64,500 against a Russian force of 90,000 to 95,000 — the French suffered higher casualties (approximately 8,000) compared to the Russian 6,000. Napoleon's intention to reinforce and press the engagement was frustrated when Bennigsen disengaged and moved toward Königsberg, preserving the Russian army's operational freedom. The battle thus failed to deliver the decisive blow Napoleon sought, though it preceded the engagement at Friedland days later, where the campaign's outcome would ultimately be settled.

The Battle of Mohrungen was a tactical engagement during the winter phase of the War of the Fourth Coalition in which Bernadotte's corps confronted a Russian advance guard under Markov near Morąg in East Prussia. Although the French initially pushed back the Russian force, a cavalry raid on the French supply train disrupted Bernadotte's offensive momentum and compelled him to break off the action. Once the raid was repelled, Bernadotte withdrew rather than renew the assault, allowing Bennigsen's army to occupy the town. The outcome left the Russians in possession of Mohrungen, reflecting the difficulties French forces faced in sustaining operational pressure against the Russian army during the demanding winter campaign in northern Poland. The engagement illustrated how flank and rear threats to logistics could neutralize tactical success on the main line, a persistent challenge in this theater.

The siege of Graudenz, lasting from January to December 1807, was one of the longest sieges of the War of the Fourth Coalition. A Prussian garrison of roughly 4,500–5,709 men under General Courbière held the fortress against a French besieging force of approximately 7,000 for eleven months, outlasting the war itself. The garrison did not capitulate even after the Peace of Tilsit formally ended hostilities between France and Prussia. The French ultimately abandoned the siege not through military reduction of the fortress but because the post-Tilsit border settlement between Prussia and the newly created Duchy of Warsaw left Graudenz within Prussian territory, rendering continued operations politically moot. The siege thus stands as an example of a garrison action that achieved its purpose through endurance rather than relief, and the fortress remained Prussian until Polish independence after the First World War.