The Battle of Petrograd, part of Napoleon's 1813 Russian Campaign, took place on April 6th, 1813 on the shore of Lake Ladoga near the Russian capital of Petrograd between the Grand Army of the French Empire, led by Napoleon I of France, against Alexander I of Russia's army. It is considered one of the greatest battles in the history of warfare, due to the previously unheard of numbers pitted against one another and the staggering loss of life - a combined 100,000 men lost their lives at Petrograd, over 61,000 of them Russians, alongside over 30,000 French and nearly 12,000 Poles and Estonians. Czar Alexander of Russia was killed at the battle and thus ended the effective organized resistance to France in Russia.
Napoleon's 1812 Invasion of Russia
Napoleon entered Russia on June 12th and quickly found himself mired down in trouble. His engagement at Smolensk was somewhat unsuccessful, although he managed to hold the city and cut off a Russian retreat. While Marshal Michel Ney pushed forward and engaged the Russians and Borodino in a vicious battle that was a hard-fought victory, Napoleon soon fell ill and was forced to retreat to Smolensk, and later to Warsaw. The Grand Army focused on opening supply lines from Poland into Smolensk, however, in order to keep the army fed through the coming winter. With Ney in charge, he elected to not enter Moscow despite being so close and retreated in early September towards Smolensk.
Alexander I, seeing this as a sign of French weakness, decided against engaging the French between Moscow and Smolensk - he ordered the Russian army regrouped and expanded in order to prepare for engagements in the spring.
Napoleon's illness improved once he returned to Paris, where his presence was needed to sate unsatisfied politicians frustrated by the Peninsula Crisis. With the bulk of his army in the East, Napoleon expanded conscription in the Confederation of the Rhine and in northern Italy in order to protect himself against what he suspected was a pending Austrian or Prussian attack to cut him off from France itself.