The Battle of Eylau (7-8 February 1807) was a major battle of the War of the Fourth Coalition during the Napoleonic Wars. The battle was fought between the armies of the First French Empire and a Russo-Prussian army at the East Prussian town of Preussisch Eylau (now Bagrationovsk, Kaliningrad Oblast, Russia).
In October 1806, Emperor Napoleon I of France defeated the Prussian army at the Battle of Jena-Auerstedt, and he proceeded to hunt down the scattered Prussians at Prenzlau, Lubeck, Erfurt, Pasewalk, Stettin, Magdeburg, and Hamelin. In late January 1807, the Russian general Levin August von Bennigsen went on the offensive in East Prussia, pushing far to the west. Napoleon reacted by conducting a counterattack to the north, hoping to prevent their retreat to the east. Bennigsen's cossacks captured Napoleon's orders, leading to Bennigsen withdrawing to the northeast to avoid being cut off. The French pursued for several days and met the combined armies of Russia and Prussia at Eylau on 7 February 1807.
The 75,000-strong French army under Emperor Napoleon I attempted to capture the village of Eylau that evening, leading to a vicious clash with the Allied armies. Both sides suffered heavy losses, and the next day brought more serious fighting. Early in that day's battle, a French frontal assault failed with catastrophic losses. The Emperor proceeded to launch a massive cavalry charge against the Russians, buying enough time for the French right wing to join the fray. The Russian left wing was bent back at an acute angle, and the Russians would have collapsed, had it not been for a Prussian corps belatedly arriving and saving the day. As darkness fell, a new French corps arrived on the army's left flank, and the Russians withdrew from the battlefield, leaving thousands of corpses and wounded men in the snow. Eylau was the first serious check to the Grande Armee and the myth of Napoleon's invincibility was badly shaken.