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Provisions and transportation

Danzig contained enough provisions to feed 400,000 men for 50 days. Breslau, Plock and Wyszogród were turned into grain depots, milling vast quantities of flour for delivery to Thorn, where 60,000 biscuits were produced every day. A large bakery was established at Villenberg (Braniewo County). 50,000 cattle were collected to follow the army. After the invasion began, large magazines were constructed at Kovno (Kaunas), Vilna (Vilnius), and Minsk, with the Vilna base having enough rations to feed 100,000 men for 40 days. It also contained 27,000 muskets, 30,000 pairs of shoes along with brandy and wine. Medium-sized depots were established at Vitebsk, Orsha, and Smolensk, and several small ones throughout the Russian interior. The French also captured numerous intact Russian supply dumps, which the Russians had failed to destroy or empty, and Moscow itself was filled with food. Twenty train battalions provided most of the transportation, with a combined load of 8,390 tons. Twelve of these battalions had a total of 3,024 heavy wagons drawn by four horses each, four had 2,424 one-horse light wagons and four had 2,400 wagons drawn by oxen. Auxiliary supply convoys were formed on Napoleon's orders in early June 1812, using vehicles requisitioned in East Prussia. Marshal Nicolas Oudinot 's II Corps alone took 600 carts formed into six companies. The wagon trains were supposed to carry enough bread, flour and medical supplies for 300,000 men for two months.

The standard heavy wagons, well-suited for the dense and partially paved road networks of Germany and France, proved too cumbersome for the sparse and primitive Russian dirt tracks, further damaged by the unstable weather. Many horses also died during the march towards Vilnius through forests which lacked the necessary fodder, slowing even further the transport of supplies for Napoleon's troops. The supply route from Smolensk to Moscow was therefore entirely dependent on light wagons with small loads. Central to the problem were the expanding distances to supply magazines and the fact that no supply wagon could keep up with a forced marched infantry column. The weather itself became an issue, where, according to historian Richard K. Riehn:

The thunderstorms of the 29th turned into other downpours, turning the tracks—some diarists claim there were no roads in Lithuania—into bottomless mires. Wagons sank up to their hubs; horses dropped from exhaustion; men lost their boots. Stalled wagons became obstacles that forced men around them and stopped supply wagons and artillery columns. Then came the sun which would bake the deep ruts into canyons of concrete, where horses would break their legs and wagons their wheels.

Jean-François Boulart reported:

Then on June 29th came a fresh and awful and extraordinary storm; such a terrible tempest had not been known in the memory of man.Thunder and lightning burst forth from every side of the horizon; soldiers were struck dead; torrents of rain flooded the bivouacs; the downpour lasted all the next day.

The heavy losses to disease, hunger and desertion in the early months of the campaign were in large part due to the inability to transport provisions quickly enough to the troops. The Intendance administration failed to distribute with sufficient rigor the supplies that were built up or captured. By that, despite all these preparations, the Grande Armée was not self-sufficient logistically and still depended on foraging to a significant extent.

Inadequate supplies played a key role in the losses suffered by the army as well. Davidov and other Russian campaign participants record wholesale surrenders of starving members of the Grande Armée even before the onset of the frosts. Caulaincourt describes men swarming over and cutting up horses that slipped and fell, even before the horse had been killed. Other accounts describe eating the flesh of horses still walking, too cold to react in pain; drinking blood and preparing black pudding was popular. The French simply were unable to feed their army. Starvation led to a general loss of cohesion. Constant harassment of the French Army by Cossacks added to the losses during the retreat.

Though starvation caused horrendous casualties in Napoleon's army, losses arose from other sources as well. The main body of Napoleon's Grande Armée diminished by a third in just the first eight weeks of the campaign, before the major battle was fought. This loss in strength was in part due to diseases such as diphtheria, dysentery and typhus and the need for garrison supply centres. There are eyewitness reports of cannibalism in November 1812.