Short answers, pulled from the story.
The French occupation of Moscow lasted from the 14th of September to the 19th of October 1812, a period of 36 days. It occurred during Napoleon's invasion of Russia and marked the furthest point of the French advance.
The most widely accepted explanation is that Governor Fyodor Rostopchin ordered the fires as a scorched earth tactic before the French arrived. He also removed or disabled all firefighting equipment in the city. Strong winds on the night of the 15th-the 16th of September fanned the flames until most of Moscow was destroyed by the 18th of September.
A police survey from the beginning of 1812 had counted 270,184 residents in Moscow. By the time the French arrived, only 6,000 to 10,000 civilians remained inside the city, along with an estimated 10,000 to 15,000 wounded and sick Russian soldiers.
Napoleon made three separate peace overtures during the occupation. He sent messages through General Tutolmin, through the landowner Ivan Yakovlev, and on the 4th of October through General Jacques Lauriston, who met with Kutuzov at Tarutino. Emperor Alexander I sent no replies to any of them.
Marshal Édouard Mortier was ordered to destroy the Kremlin before the French retreated in October 1812. The Vodovzvodnaya Tower was completely destroyed, and the Nikolskaya, 1st Bezymyannaya, and Petrovskaya Towers, along with the Kremlin wall and part of the arsenal, were badly damaged. The Ivan the Great Bell Tower, the city's tallest structure, survived nearly unharmed.
Moscow required more than half a century to rebuild and return to its pre-war population of 270,184 residents. The imperial manifesto of the 30th of August 1814 granted amnesty for most crimes committed during the invasion, but physical reconstruction of the city took far longer.