On the 7th and 8th, February 1807 the Battle of Eylau took place, between the forces of Napoleon I and the Russian army.
After the battles of Austerlitz and Jena-Auerstädt, Napoleon occupied the German cities and marched eastward, entering Poland with little resistance. The battle began when the French forces moved forward to occupy the town of Eylau, where the Russian army was located. It quickly spread into a long and bitter confrontation that continued into the night.
At dawn there was almost no visibility and the dense storm clouds continued throughout the day. The enemy forces occupied two parallel crests, and shortly after 8:00 they began the artillery duel.
After 14 hours of continuous battle, the Russian army began to retreat stealthily, but the French did not realize it until 4 hours later and were not in a position to initiate the persecution. Technically, the French have gained possession of the battlefield, but they had suffered enormous losses and failed to destroy the Russian army.
original post published by DENIX on their website