The first Battle of Smolensk was a battle during the second phase of Operation Barbarossa, the Axis invasion of the Soviet Union, in World War II. It was fought around the city of Smolensk between 10 July and 10 September 1941, about 400 km (250 mi) west of Moscow. The Ostheer had advanced 500 km (310 mi) into the USSR in the 18 days after the invasion on 22 June 1941.