Karelian Isthmus, a strip of land about 90 miles (145 km) long and up to 70 miles (110 km) wide, lying between the Gulf of Finland and the western shore of Lake Ladoga, in Russia. St. Petersburg is near its southern end. A strategic borderland between Finland and the Soviet Union, it was the scene of heavy fighting in World War II. It was ceded to the Soviet Union by the Finns in 1944, becoming a part of the Russian Soviet Federated Socialist Republic.