On 14 October 1806, Napoleon crushed the armies of the Kingdom of Prussia at the Battle of Jena–Auerstedt and hunted down the scattered Prussians at Prenzlau, Lübeck, Erfurt, Pasewalk, Stettin, Magdeburg and Hamelin.

That night, Bennigsen decided to retreat, leaving Napoleon in possession of a snowy battlefield covered with thousands of dead and wounded.

With the Prussian army routed at Jena-Auerstedt, Napoleon occupied the major cities of Germany and marched east in pursuit of the remaining forces opposed to him.

The old marshal was unwilling to risk battle and continued to retreat, leaving the Grande Armée free to enter Poland almost unopposed.

Tough fighting at the Battle of Mohrungen allowed Bernadotte's corps to escape serious damage and pull back to the southwest.

By a stroke of luck, a band of Cossacks captured a messenger carrying Napoleon's plans to Bernadotte and quickly forwarded the information to General Pyotr Bagration.

Bernadotte was left unaware, and a forewarned Bennigsen immediately ordered a retreat east to Jonkowo to avoid the trap.

As Bennigsen hurriedly assembled his army at Jonkowo, elements of Marshal Nicolas Soult's IV Corps reached a position on his left rear on 3 February.

During the pursuit, perhaps influenced by the dreadful state of the Polish roads, the savage winter weather and the relative ease with which his forces had dealt with Prussia, Napoleon had allowed the Grande Armée to become more spread out than was his custom.

During the afternoon, the French were reinforced by Marshal Augereau's corps and the Imperial Guard, giving him a force of about 45,000 soldiers in all.

Napoleon later claimed that was on his orders and that the advance had the dual aims of pinning the Russian force to prevent it from retreating yet again and of providing his soldiers with at least some shelter against the terrible cold.

Other surviving evidence, however, strongly suggests that the advance was unplanned and occurred as the result of an undisciplined skirmish, which Marshals Soult and Murat should have acted to quell but failed to do so.

Whatever the cause of the fight for the town, it rapidly escalated into a large and bitterly fought engagement, continuing well after night had fallen and resulting in about 4,000 casualties to each side, including Barclay, who was shot in the arm and forced to leave the battlefield.

Both sides did without food—the Russians because of their habitual disorganization, the French because of problems with the roads, the weather and the crush of troops hurrying towards the battle.

One regiment, the 14th Ligne, was unable to retreat and fought to the last man, refusing to surrender; its eagle was carried off by Captain Marbot.

[20] Bennigsen took full advantage by falling on Saint-Hilaire's division with more cavalry and bringing up his reserve infantry to attack the devastated French centre.

At one point, Napoleon himself, using the church tower as a command post, was nearly captured, but members of his personal staff held the Russians off for just long enough to allow some battalions of the Guard to come up.

The group on the right, Grouchy's dragoons, charged into the flank of the Russian cavalry attacking Saint-Hilaire's division and scattered them completely.

A second wave of cavalry consisting of the Guards, and Grouchy's dragoons now charged the Russians as they attempted to reform and rode through both lines of infantry.

Murat had lost 1,000–1,500 well-trained troopers[23] but relieved the pressure on Augereau, Saint-Hilaire and Soult, paralyzing the Russians long enough to allow Davout to deploy in strength.

That was in part because for the first time, Murat's men were now mounted on the best cavalry horses in Europe, which had been freshly requisitioned in the aftermath of the conquest of Prussia.

Such a move might have decisively won the battle, but Napoleon, well aware that 9,000 Prussians under L'Estocq and his chief of staff, Gerhard von Scharnhorst were still unaccounted for, judged it wise to retain the Guard in reserve.

Although Ney was within marching distance of the battle, the heavy snow had muffled the sound of cannon fire, and he was completely unaware of the events until a messenger reached him around 10:30.

After a contentious council of war in which several of his generals forcefully argued for continuing the fight for a third day, Bennigsen at 23:00 decided to withdraw, and covered by the Cossacks, the Russians silently began to leave.

Authors differ greatly in their assessments of the relative losses: estimates of Russian casualties range from about 15,000[10][11] to 20,000 killed or wounded and 3,000 men, 23 cannon and 16 colors captured.

[3] According to estimates of the German historian Horst Schulz, the French lost 4,893 men killed, 23,598 wounded and 1,152 missing in action, for a total of 29,643.

[9] The French had gained possession of the battlefield, which was nothing but a vast expanse of bloodstained snow and frozen corpses, but they had suffered enormous losses and failed to destroy the Russian army.

[30] Hostilities continued until the decisive French victory at the Battle of Friedland in June 1807 forced Tsar Alexander I to the negotiating table.

The surgeon-in-chief of Napoleon's Grand Army, Baron Dominique-Jean Larrey, served the wounded with the flesh of young horses as soup and bœuf à la mode.

The brutal battle and its immediate aftermath are depicted from the point of view of an ordinary soldier, a Prussian cavalry sergeant, who is severely wounded by a French saber in the later part of the confused fighting and whose only chance of saving his life is to desert and find shelter with Polish peasants in the neighborhood.