The main Russian army retreated for almost three months. This constant retreat led to the unpopularity of Field Marshal Michael Andreas Barclay de Tolly and a veteran, Prince Mikhail Kutuzov, was made the new Commander-in-Chief by Tsar Alexander I. Finally, the two armies engaged in the Battle of Borodino on 7 September, in the vicinity of Moscow. The battle was the largest and bloodiest single-day action of the Napoleonic Wars, involving more than 250,000 men and resulting in at least 70,000 casualties. It was indecisive; the French captured the main positions on the battlefield, but failed to destroy the Russian army. Logistical difficulties meant that French casualties could not be replaced, unlike Russian ones.