On June 24 in 1812, Napoleon's huge "Grande Armée" crossed the Neman river and invaded Russia. That wasn't a good idea BTW, seeing how only about 150,000 Napoleonic troops out of 650,000 would make the return journey back from Russia.
The Russians, after suffering defeat in the battle of Borodino, resorted to "scorched earth" policies and would even later burn down their own capital, Moscow, and forced the French army to face the Russian winter without any supplies and proper shelter.
Although it never lost a pitched battle in Russia, Napoleon and the Grande Armée were almost completely wiped out within six months by freezing temperatures, food shortages, disease and Russian assaults.
This proved to be the beginning of the end for Napoleon, who was forced into exile in April 1814.