After driving off the cavalry, Bernadotte withdrew and the town was occupied by the army of General Levin August, Count von Bennigsen.

After demolishing the army of the Kingdom of Prussia in a whirlwind campaign in October and November 1806, Napoleon's Grande Armée seized Warsaw.

After two bitterly fought actions against the Russian army, the French emperor decided to place his troops into winter quarters.

However, in wintry weather, the Russian commander moved north into East Prussia and then struck west at Napoleon's left flank.

[2] Emperor Napoleon wanted time to reorganize the Grande Armée's logistical arrangements after their long autumn campaign.

[3] In late 1806, Field Marshal Mikhail Kamensky's Russian army in Poland constituted two major wings under Generals Bennigsen and Friedrich Wilhelm von Buxhoeveden (Buxhöwden).

The initial strength of Bennigsen's force, before the December battles, was 49,000 infantry, 11,000 regular cavalry, 4,000 cossacks, 2,700 artillerymen, 900 pioneers, and 276 guns.

They intended to move north into East Prussia with seven divisions before turning west to attack Napoleon's left flank.

[15] The Russian leaders hoped to damage Napoleon's left wing and force the French army to fall back to the west bank of the Vistula.

[16] Still jealous of his rival Buxhöwden, Bennigsen withdrew east to Tykocin with his six divisions rather than join his troops to the right wing of the army.

He marched north for Goniądz where he found, to his delight, that Czar Alexander had appointed him army commander and recalled Buxhöwden.

The Prussian field force under General-Leutnant Anton Wilhelm von L'Estocq withdrew northward to Rastenburg (Kętrzyn).

[17] Meanwhile, Ney, finding his sector devoid of food and forage, disobeyed Napoleon's orders and advanced far northward in the direction of Königsberg.

Three days later, Ney estimated that L'Estocq had 9,000 troops while General of Infantry Ernst von Rüchel garrisoned Königsberg with another 4,000.

[18] Livid at Ney for his insubordination, Napoleon nevertheless began to take measures in case the Russians reacted to the VI Corps leader's advance.

The emperor also ordered Marshal François Joseph Lefebvre and the X Corps to protect Thorn (Toruń) and the lower Vistula.

The three Russian advance guards were led by Major Generals Markov, Michael Andreas Barclay de Tolly, and Karl Gustav von Baggovut.

Though his cavalry under General of Brigade Auguste Francois-Marie de Colbert-Chabanais was roughly handled, Ney managed to escape southward to Neidenburg (Nidzica).

On his own initiative, Bernadotte's chief of staff General of Brigade Nicolas Joseph Maison alerted the I Corps center and right flank.

General of Division Jean Baptiste Eblé led four-foot and two horse artillery batteries, a total of 36 guns.

General of Brigade Jacques Louis François Delaistre de Tilly led the corps cavalry, the 2nd and 4th Hussar and 5th Chasseurs à Cheval Regiments.

Golitsyn, leading the cavalry of the left wing, reached the village of Alt Reichau (Boguchwały), east of Mohrungen.

The Russian horsemen entered Mohrungen as night fell, capturing the few defenders and pillaging the baggage trains that they found in the town.

[27] Trying to exploit their success, Dolgorukov and Pahlen moved north where they bumped into Bernadotte's returning troops and quickly retreated.

[35] At L'Estocq's approach, Rouyer raised the siege, allowing the Prussians to restock the garrison's food supplies on 31 January.

[35] A Russian advance guard under General Pyotr Bagration linked L'Estocq and Bennigsen's main force, which was centered on Mohrungen, facing south.

[36] Napoleon saw that Bennigsen had advanced so far west that there was an opportunity to hit the Russian army in the left flank and rear.

Napoleon ordered the corps of Davout, Soult, Augereau, Murat, and the Imperial Guard northward to Allenstein, while Ney covered the gap between the main body and Bernadotte.