In June 1812, Napoleon's "Grand Army" -- at 600,000 men one of the largest in human history -- confidently entered Russia.
But they were woefully unprepared for the harsh weather, the strong Russian defense and the Russian scorched-earth tactics, which left nothing behind to sustain the hungry and freezing French troops.
"This letter is an incredible insight, we never see Napoleon emotively speaking in this way before," says Chataignier.
"Only in letters to (his wife) Josephine did he ever express anything near to emotion. Moscow knocked him."
In the text -- which announces that his commanders are evacuating Moscow -- Napoleon laments his army's plight, asking for assistance to replenish his forces and the ravaged cavalry, which saw thousands of horses die.
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