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Cold weather

Following the campaign, a saying arose that "General Winter" defeated Napoleon, alluding to the Russian Winter. Minard's map shows that the opposite is true as the French losses were highest in the summer and autumn, due to inadequate preparation of logistics resulting in insufficient supplies, while many troops were also killed by disease. Thus, the outcome of the campaign was decided long before the cold weather became a factor.

When winter arrived on 6 November with a blizzard, the army was still equipped with summer clothing and did not have the means to protect themselves from the cold or snow. It had also failed to forge caulkin shoes for the horses to enable them to traverse roads that had become iced over. The most devastating effect of the cold weather upon Napoleon's forces occurred during their retreat. Starvation and gangrene coupled with hypothermia led to the loss of tens of thousands of men. Heavy artillery pieces, loot, and wagons were abandoned as irreplaceable draft animals perished. The intense cold enfeebled the brains of those whose health had already suffered, especially of those who had had dysentery, but soon, while the cold increased daily, its pernicious effect was noticed in all.

In his memoir, Napoleon's close adviser Armand de Caulaincourt recounted scenes of massive loss, and offered a vivid description of mass death through hypothermia:

The cold was so intense that bivouacking was no longer supportable. Bad luck to those who fell asleep by a campfire! Furthermore, disorganization was perceptibly gaining ground in the Guard. One constantly found men who, overcome by the cold, had been forced to drop out and had fallen to the ground, too weak or too numb to stand. Ought one to help them along—which practically meant carrying them. They begged one to let them alone. There were bivouacs all along the road—ought one to take them to a campfire? Once these poor wretches fell asleep they were dead. If they resisted the craving for sleep, another passer-by would help them along a little farther, thus prolonging their agony for a short while, but not saving them, for in this condition the drowsiness engendered by cold is irresistibly strong.

This befell a Grande Armée that was ill-equipped for cold weather. The French deficiencies in equipment caused by the assumption that their campaign would be concluded before the cold weather set in were a large factor in the number of casualties they suffered. After a few days of thaw, the temperature dropped again 23 November. From the Berezina, the retreat was nothing but utter flight. The preservation of war materiel and military positions was no longer considered. When the night-time temperature dropped to minus 35 degrees Celsius it proved catastrophic for Loison's untried soldiers. Some suffered from snow blindness. Within three days, his division of 15,000 soldiers lost 12,000 men without a battle.