When the Grande Armée crossed into Russia in June, they split their forces with some heading north, others east (with Napoleon) and some to the south. The Russians had a number of different armies and Napoleon wanted to make sure they were all covered.
On July 21, Marshal Louis Nicolas Davout made contact with advance elements of Prince Pyotr Bagration’s 2nd army. The terrain of the impending battle favored the French with a field surrounded by forests and a deep ravine with a stream along the bottom. This would prevent the Russians from bringing their numerical superiority to bear on an open field.
Davout spend the night of the 22nd preparing the field of battle. He had one bridge barricaded while the sappers (engineers) took down a bridge and a dam. They also cut loopholes in the neighboring buildings. The attack by the Russians would come the next morning.