Mannerheim line

Mannerheim Line
Karelian Isthmus
The Mannerheim Line from the Gulf of Finland to Lake Ladoga
Type	Defensive line
Site information
Controlled by	Finland
Site history
Built	1920–1924, 1932–1939
In use	1939–1940
Materials	Wood, boulders, concrete, steel, natural features
Battles/wars	Winter War

The Mannerheim Line (Finnish: Mannerheim-linja, Swedish: Mannerheimlinjen) 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. By November 1939, when the Winter War began, the line was by no means complete.

After the October Revolution in Russia, the Finns declared independence in 1917. Although Soviet Russia recognized Finland's independence, the Finns did not trust their sincerity. The relationship between the two countries deteriorated, with Soviet Russia supporting the Red Guard during the Finnish Civil War in 1918. After the victory of the White Guard, a group of Finnish communists fled to Soviet Russia and established the Communist Party of Finland.

Generally, communism was seen as a threat to a democratic system. The situation was dangerous for a new nation like Finland, especially as the capital of the new communist revolution was nearby Petrograd, (now Saint Petersburg). Furthermore, before the Treaty of Tartu in 1920, the border area was restless. The former general of Imperial Russia, C.G.E. Mannerheim, strongly opposed the bolsheviks. During the Russian Civil War, in 1919, the Finns even considered supporting an assault of the White Guards on Petrograd, but this plan was abandoned as the military situation in the Russian Civil War changed (the Finns also did not believe that the Whites would uphold Finland's independence). Construction work on the Karelian Isthmus had already begun when the Bolsheviks won the Russian Civil War in 1922. The line was constructed in two phases: 1920–1924 and 1932–1939.