According to Chew in 1981, the main body of Napoleon's Grande Armée, initially at least 378,000 strong, "diminished by half during the first eight weeks of his invasion, before the major battle of the campaign. This decrease was partly due to garrisoning supply centres, but disease, desertions, and casualties sustained in various minor actions caused thousands of losses. At the Battle of Borodino on 7 September 1812—the only major engagement fought in Russia—Napoleon could muster no more than 135,000 troops and he lost at least 30,000 of them to gain a narrow and pyrrhic victory almost 600 miles inside hostile territory.