During the French occupation of Moscow, a fire persisted from 14 to 18 September 1812 and destroyed the city. The Russian troops and most of the remaining civilians had abandoned the city on 14 September 1812 just ahead of French Emperor Napoleon's troops entering the city after the Battle of Borodino. The Moscow military governor, Count Fyodor Rostopchin, has often been considered responsible for organising the destruction of the former capital to weaken the French army in the scorched city even more.
Background
After continuing Barclay's "delaying operation" as part of his attrition warfare against Napoleon, Kutuzov used Rostopchin to burn most of Moscow's resources as part of a scorched earth strategy, guerilla warfare by the Cossacks against French supplies and total war by the peasants against French foraging. This kind of war without major battles weakened the French army at its most vulnerable point: military logistics. On 19 October 1812, the French army, lacking provisions and being warned by the first snow, abandoned the city voluntarily.
Regarding the state of Moscow itself, the city was mostly deserted, at least in comparison to its normal levels of population: At the beginning of 1812 Moscow had around 270,184 inhabitants according to a contemporary police survey; of these, somewhere between 6,200 and 10,000 civilians chose to remain in the city after the arrival of the French, in addition to between 10,000 and 15,000 sick or wounded Russian soldiers.
Causes
Search had been made for the fire-engines since the previous day, but some of them had been taken away and the rest put out of action...The Poles reported that they had already caught some incendiaries and shot them, ...they had extracted the information that orders had been given by the Governor of the city and the police that the whole city should be burnt during the night.
Before leaving Moscow, Count Rostopchin supposedly gave orders to the head of police (and released convicts) to have the Kremlin and major public buildings (including churches and monasteries) set on fire. During the following days, the fires spread. According to Germaine de Staël, who left the city a few weeks before Napoleon arrived and afterward corresponded with Kutuzov, it was Rostopchin who ordered his own mansions to be set on fire, so no Frenchmen should lodge in it. The French actress Louise Fusil, who was living in Moscow, wrote that the fire started at Petrovka Street and offers more details in her memoirs. Today, the majority of historians blame the initial fires on the Russian strategy of scorched earth.
Furthermore, a Moscow police officer was captured trying to set the Kremlin on fire where Napoleon was staying at the time. Brought before Napoleon, the officer admitted he and others had been ordered to set the city on fire, after which he was bayonetted by guardsmen on the spot on the orders of a furious Napoleon.
The sight of the fire deeply disturbed Napoleon who was horrified and intimidated at the Russian resolution to destroy their most sacred and beloved city before surrendering it. According to him, most churches, monasteries, and palaces survived as they were made out of stone. A witness records him as remaining transfixed watching the fire from the Kremlin while saying: "What a terrible sight! And they did this themselves! So many palaces! What an incredible solution! What kind of people! These are Scythians!"
The catastrophe started as many small fires, which promptly grew out of control and formed a massive blaze from the northeast, according to Larrey. The fires spread quickly since most buildings in Moscow were made of wood, except in the German Quarter. Although Moscow had a fire brigade, their equipment had previously either been removed or destroyed on Rostopchin's orders. The flames spread into the Kremlin's arsenal, and was put out by French guardsmen. The burning of Moscow is reported to have been visible up to 200 versts (215 km, or 133 miles) away.
Tolstoy, in his book War and Peace, suggests that the fire was not deliberately set, neither by the Russians nor the French, but was the natural result of placing a deserted and mostly wooden city in the hands of invading troops. Before the invasion, fires would have started nearly every day even with the owners present and a fully functioning fire department, and the soldiers would start additional fires for their own needs, from smoking their pipes, cooking their food twice a day, and burning enemies' possessions in the streets. Some of those fires would inevitably get out of control, and without an efficient firefighting response, these individual building fires would spread to become neighborhood fires, and ultimately a citywide conflagration.