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

These were largely Russians under the command of the frail sixty-eight-year-old Field Marshal Count Mikhail Kamensky.

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

Nevertheless, as the French pressed aggressively eastward across the Vistula, they had  found the Russians defending the line of the Wkra River.

The French had seized a crossing over the Wkra on December 23 at the Battle of Czarnowo.

Russian resistance had soon stiffened and on December 26, the two armies clashed at the Battles of Pułtusk and Gołymin.

The result remained in doubt, but Levin August, Count von Bennigsen, had written to the Tsar that he had defeated sixty thousand French troops, and as a result had gained overall command of the Russian armies in Poland.

After these fierce engagements, Napoléon's troops had taken took up winter quarters in Poland to recuperate after a victorious but exhausting campaign.
 
In January 1807, Bennigsen attempts to surprise the French left wing by shifting the bulk of his army north from Nowogród to East Prussia.

Incorporating a Prussian corps on his right flank, he first bumps into elements of the VI Corps of Marshal Michel Ney, who had disobeyed his emperor's orders and advanced far north of his assigned winter cantonments.

Having cleared Ney's troops out of the way, the Russians roll down on the isolated French I Corps under Marshal Jean-Baptiste Bernadotte.

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

With his customary inventiveness, Napoléon sees an opportunity to turn the situation to his own advantage.

He instructs Bernadotte to withdraw before Bennigsen's forces, and orders the balance of the Grande Armée to strike northward.

This maneuver might envelop the Russian army's left flank and cut off its retreat to the east.

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

At once Bernadotte is left unawares and a forewarned Bennigsen immediately orders a retreat east to Jonkowo to avoid the trap.

The Russians withdraw towards Allenstein, and later to Eylau.

The Russian army is in full retreat by early February, relentlessly pursued by the French.

After several aborted attempts to stand and fight, Bennigsen resolves to retreat to the town of Preussisch-Eylau and here make a stand.

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, Napoléon had allowed the Grande Armée to become more spread out than was his custom.

In contrast, Bennigsen's forces are already concentrated.

The Russians fight Soult's corps for possession of Eylau on February 7.

Daybreak on February 8 sees forty-four thousand five hundred  French troops on the field against sixty-seven thousand Russians, but after receiving reinforcements the French had seventy-five thousand men against seventy-six thousand.

Napoleon hopes to pin Bennigsen's army long enough to allow Ney's and Davout's troops to outflank the Russians.

A fierce struggle ensues, made worse by a blinding snowstorm on the battlefield.

The French find themselves in dire straits until a massed cavalry charge, made by ten thousand seven hundred troopers formed in eighty squadrons, relieves the pressure on the center.

Davout's arrival means the attack on the Russian left can commence, but the assault is blunted when a Prussian force under Lestoq suddenly appears on the battlefield and, with Russian help, throws the French back.

Ney comes too late to effect any meaningful decision, so Bennigsen retreats.

After fourteen hours of continuous battle, there is still no result but enormous loss of life.

Casualties at this indecisive battle are horrific, perhaps twenty-five thousand on each side.

More importantly, however, the lack of a decisive victory by either side means that the war will go on

Authors differ greatly in their assessments of the relative losses: estimates of Russian casualties range from about fifteen thousand to twenty thousand killed or wounded and three thousand soldiers, twenty-three cannon and sixteen colors captured.

Count von Bennigsen estimates his losses at up to nine thousand dead and seven thousand wounded.

The French lose somewhere between ten thousand to fifteen thousand and twenty-five thousand to thirty thousand, with five Eagles lost.

The French have gained possession of the battlefield—nothing but a vast expanse of bloodstained snow and frozen corpses—but they have suffered enormous losses and failed to destroy the Russian army.

The inconclusive Battle of Eylau is a major contrast to the decisive victories that had characterized Napoleon's earlier campaigns.

By halting the French advance and leaving the two sides exhausted but evenly matched, it serves only to prolong the war.

The tactical draw at Eylau on February 7 and 8 had forced the Russians to withdraw further north.

After the battle, Napoleon had sent General Bertrand to the King of Prussia to offer a separate peace, which would see French forces withdraw from Prussia and her borders completely restored.

Prussia, wishing to continue its alliance with Russia, had quickly rejected this offer.

On May 24, 1807, the six-week Siege of Danzig ends when Prussian General Friedrich Adolf, Count von Kalckreuth, capitulates to French Marshal François Joseph Lefebvre.

Napoleon now orders the siege of the nearby Weichselmünde fort, but Kamensky had fled with his troops, and the garrison capitulates shortly afterwards.

The battle has cost the French six thousand killed and wounded, while the Prussians have lost three thousand killed, wounded and sick, and the Russians fifteen hundred.

In recompense for Lefebvre's services, Napoléon will grante him the title “Duc de Dantzig” in a letter to the Senate dated May 28.

With Danzig (modern day Gdańsk) secured, Napoleon is now free to turn against Bennigsen's army, yet it is the Russian who had struck first when he ordered his columns to converge on Marshal Michel Ney's exposed VI Corps on June 2.

Outnumbered sixty-three thousand to seventeen thousand, Ney fights a rear guard action at the Battle of Guttstadt-Deppen on June 5 and 6.

Though he loses his baggage train, two guns, and two thousand and forty-two men, Ney manages to escape to the southwest over the Pasłęka (Passarge) River with the bulk of his soldiers, leaving Bennigsen and his officers upset over the missed opportunity.

Within two days, Napoleon orders his one hundred and ninety thousand-man army to close in on the one hundred thousand Russians and fifteen thousand Prussians.

Detecting the approaching avalanche, Bennigsen orders his troops to retreat on Lidzbark Warmiński (Heilsberg).

Napoleon, after several months of recuperating from Eylau, orders the Grande Armée on the move once again.

Learning that the Russians have encamped at their operational base in the town of Heilsberg, by the Alle River, Napoleon decides to conduct a general assault in the hopes of dislodging what he thinks is the rearguard of the Russian army.

In fact, the French run into the entire Russian army of over fifty thousand men and one hundred and fifty artillery guns.

Repeated and determined attacks by the French fail to dislocate the Russians, who are fighting inside elaborate earthworks designed to prevent precisely the kind of river crossing Napoleon is attempting.

French casualties soar to ten thousand while the Russians lose about six thousand.

The Russians eventually withdraw from Heilsberg as their position becomes untenable, prompting Napoleon to chase after them once again.

The French head in the direction of Königsberg to gain additional supplies and provisions.

The advance guard of Marshal Lannes reports seeing large numbers of Russian troops at the town of Friedland on June 13.

Both sides engage one another for the remainder of the day with no result.

Crucially, Bennigsen believes he has enough time to cross the Alle the following day, to destroy the isolated units of Lannes, and to withdraw back across the river without ever encountering the main French army.

Bennigsen's main body begins to occupy the town on the night of June 13, after Russian forces under General Golitsyn have driven off the French cavalry outposts.

The army of Napoleon marches on Friedland, but remains dispersed on its various march routes, and the first stage of the engagement becomes a purely improvisational battle.

Knowing that Napoleon is within supporting distance with at least three corps, Lannes sends aides galloping off with messages for help and wages an expert delaying action to fix Bennigsen in place.

With never more than twenty-six thousand men, Lannes forces Bennigsen to commit progressively more troops across the Alle to defeat him.

The French, showing a bold front, and shifting troops where needed to stop Russian advances, engage the Russians first in the Sortlack Wood and in front of Posthenen in the early hours of the 14th.

Lannes holds Bennigsen in place until the French have massed eighty thousand troops on the left bank of the river.

Both sides now use their cavalry freely to cover the formation of lines of battle, and a race between the rival squadrons for the possession of Heinrichsdorf ends in favor of the French under Grouchy and Nansouty.

Bennigsen is trapped and has to fight.

Having thrown all of his pontoon bridges at or near the bottleneck of the village of Friedland, Bennigsen has unwittingly trapped his troops on the west bank.

In the meantime Lannes fights hard to hold Bennigsen.

Napoleon fears that the Russians mean to evade him again, but by 6 a.m. Bennigsen hasd nearly fifty thousand men across the river and forming up west of Friedland.

His infantry, organized in two lines, extends between the Heinrichsdorf-Friedland road and the upper bends of the river along with the artillery.

Beyond the right of the infantry, cavalry and Cossacks extend  the line to the wood northeast of Heinrichsdorf.

Small bodies of Cossacks penetrate even to Schwonau.

The left wing also has some cavalry and, beyond the Alle river, batteries come into action to cover it.

A heavy and indecisive fire-fight rages in the Sortlack Wood between the Russian skirmishers and some of Lannes's troops.

The head of Mortier's (French and Polish) corps appears at Heinrichsdorf and drives the Cossacks out of Schwonau.

Lannes holds his own, and by noon Napoleon arrives with forty thousand French troops at the scene of the battle.

Napoleon gives brief orders: Ney's corps will take the line between Postlienen and the Sortlack Wood, Lannes closing on his left, to form the center, Mortier at Heinrichsdorf the left wing.

I Corps under General Victor and the Imperial Guard are placed in reserve behind Posthenen.

Cavalry masses are collected at Heinrichsdorf.

The main attack is to be delivered against the Russian left, which Napoleon sees at once to be cramped in the narrow tongue of land between the river and the Posthenen mill-stream.

Three cavalry divisions are added to the general reserve.

The course of the morning's operations means that both armies still have large detachments out towards Königsberg.

The emperor spends the afternoon in forming up the newly arrived masses, the deployment being covered by an artillery bombardment.

At 5 o'clock all is ready, and Ney, preceded by a heavy artillery fire, rapidly carries the Sortlack Wood.

The attack is pushed on toward the Alle.

Marshal Ney's right-hand division under Marchand drives part of the Russian left into the river at Sortlack, while the division of Bisson advances on the left.

A furious charge by Russian cavalry into the gap between Marchand and Bisson is repulsed by the dragoon division of Latour-Maubourg.

Soon the Russians find themselves huddled together in the bends of the Alle, an easy target for the guns of Ney and of the reserve.

Ney's attack indeed comes eventually to a standstill; Bennigsen's reserve cavalry charges with great effect and drives him back in disorder.

As at Eylau, the approach of night seems to preclude a decisive success, but in June and on firm ground the old mobility of the French reasserts its value.

The infantry division of Dupont advances rapidly from Posthenen, the cavalry divisions drive back the Russian squadrons into the now congested masses of infantry on the river bank, and finally the artillery general Sénarmont advances a mass of guns to case-shot range.

The terrible effect of the close range artillery sees the Russian defense collapsing within minutes, as canister decimates the ranks.

Ney's exhausted infantry succeeds in pursuing the broken regiments of Bennigsen's left into the streets of Friedland.

Lannes and Mortier have meanwhile held the Russian center and right on its ground, and their artillery has inflicted severe losses.

When Friedland itself is seen to be on fire, the two marshals launch their infantry attack.

Fresh French troops approach the battlefield.

Dupont distinguishes himself for the second time by fording the mill-stream and assailing the left flank of the Russian center.

This offers stubborn resistance, but the French steadily forces the line backwards, and the battle is soon over.

The Russians suffer heavy losses in the disorganized retreat over the river, with many soldiers drowning.

Farther north, the still unbroken troops of the right wing withdraw by using the Allenburg road; the French cavalry of the left wing, though ordered to pursue, remains inactive.

French casualties number approximately ten thousand soldiers, while the Russians suffer at least twenty thousand casualties.

Emperor Alexander had sent an envoy to seek an armistice with the French on June 19.

Napoleon had assured the envoy that the Vistula River represents the natural borders between French and Russian influence in Europe.

On that basis, the two emperors had begun peace negotiations at the town of Tilsit after meeting on an iconic raft on the River Niemen.

The very first thing Alexander said to Napoleon was probably well-calibrated: "I hate the English as much as you do."

Napoleon had reportedly replied, "Then we have already made peace."

The two emperors spend several days reviewing each other's armies, passing out medals, and frequently talking about non-political subjects.

Although the negotiations at Tilsit feature plenty of pageantry and diplomatic niceties, they are not spared from ruthless politics.

Alexander faces pressure from his brother, Duke Constantine, to make peace with Napoleon.

Given the victory he had just achieved, the French emperor offers the Russians relatively lenient terms–demanding that Russia join the Continental System, withdraw its forces from Wallachia and Moldavia, and hand over the Ionian Islands to France.

By contrast, Napoleon dictates very harsh peace terms for Prussia, despite the ceaseless exhortations of Queen Louise.