It is fairly well documented that Napoleon's retreat from Moscow in 1812 was somewhat slowed by the large amounts of civilians following the army. My question is - where did these civilians come from and why did the Grand Army accommodate them? What happened to them when they were captured by the Russians?
They are termed camp followers and have followed armies since before Ramses II at Kadesh. Modern armies travel with long tails of official logistical services - cooks, tailors, smiths, armourers, teamsters, nurses, physicians & surgeons, etc. - that in earlier times were provided by civilian camp followers, but wives, children, mistresses and others have also been present since time immemorial.
American armies has been more prudish than most in their regard (notably only after the Revolutionary War), and European armies in general have usually declined to officially supply comfort women to their troops. However armies have always been a profitable place to find lonely young men with money to burn, especially after a victory. Wives have often found it worthwhile to follow their men to guard their husbands from temptation and share their tribulations, as Martha Washington did at Valley Forge. Marshal Massena's mistress always followed a day or two behind her husband while on campaign, except when accompanying him more directly dressed as a male soldier.
and during the retreat from Moscow (my emphasis):
In the Waterloo Campaign Napoleon lost patience with the camp followers, and both authorized and directed (pages 268-272) his Director-Genera of Transport to burn all vehicles which hindered troop and baggage movements: