Fragments of the Mannerheim Line on the shore of Lake Syuskyuvi, Karelia.

The Mannerheim Line was a defensive fortification line on the Karelian Isthmus built by Finland against the Soviet Union. During the Winter War it became known as the Mannerheim Line, after Field Marshal Baron Carl Gustaf Emil Mannerheim. The line was constructed in two phases: 1920–1924 and 1932–1939.