The First Battle of Kiev or Kiev operation, known as the Battle of Kiev on the German side, was a major battle that resulted in an encirclement of Soviet troops in the vicinity of Kiev during World War II, the capital and most populous city of the Ukrainian Soviet Socialist Republic. This encirclement is the largest in the history of warfare by number of troops. The battle lasted from 7 July to 26 September 1941 as part of Operation Barbarossa, the Axis invasion of the Soviet Union. Although it is known as the "Battle of Kiev", the city played only a peripheral role in the overall battle; for the Soviets, a strategic defensive operation. The battle took place over a large area in eastern Ukraine, with Kiev being the focal point of Soviet defenses and of the German encirclement.