Salpa line

 
THE LARGEST CONSTRUCTION PROJECT IN THE HISTORY OF INDEPENDENT FINLAND
The Winter War between Finland and the Soviet Union took place in 1939–1940. As a result of the war, Finland lost some areas but retained its independence. Despite the peace treaty, a new war was likely. Finland had lost terrain useful for defending its eastern border as the border moved westwards, and the decision was made to protect the new border by constructing the Salpa Line, a line of defence extending from the Gulf of Finland to the province of Petsamo.
 
The construction work began in April 1940 in Virolahti by the Gulf of Finland. The work was interrupted when the Continuation War between Finland and the Soviet Union started in June 1941. After a short defensive phase, the Finns started an offensive to gain back areas lost in the Winter War, and the Salpa Line was left far behind the front. Fortification work concentrated on the front lines and behind them. When the Soviet Union started its major offensive on the Karelian Isthmus in June 1944, the Salpa Line was seen as an important defensive line that had to be prepared for battle as soon as possible. The Finns brought the Soviet offensive to a standstill by mid-July 1944, so the strength of the Salpa Line was not tested in battle after all. Nevertheless, it had an indirect effect on the events towards the end of the Continuation War. The Salpa Line was declared Finland’s main defensive line right before the armistice in September 1944.
At the end of the fortification work, the defensive line comprised 728 reinforced concrete bunkers, 3,000 wooden field fortifications, about 225 km of multi-row anti-tank lines and more than 300 km of barbed-wire obstacles. More than 350 kilometres of battle and communication trenches were dug. At the most, the fortification work involved as many as 35,000 hired civilians in addition to army troops. 
With a total length of 1,200 km, the Salpa Line is one of Europe’s strongest and best-preserved World War II fortification lines.
 
THE SALPA LINE TODAY
Fortification work on the Salpa Line ended after the end of the Continuation War in 1944, but the Finnish Defence Forces maintained the fortifications until the 1980s. In 2003, the Salpa Line was transferred from the Ministry of Defence to the Ministry of Finance, and the fortifications are nowadays taken care of by Senate Properties. With the development of military technology, the fortifications have lost their military significance, and focus has been placed on their tourism and recreational values. Some of the fortifications have been refurbished and taken into museum and tourism use. Today, the Salpa Line is comparable with sites protected under the Antiquities Act.
Right after the Continuation War, some of the Salpa Line’s wooden field fortifications and barbed-wire obstacles were taken down and used as construction supplies. In the course of time, a small number of the stone obstacles have been cleared and some trenches and anti-tank ditches filled to make it easier to get around, cultivate land and conduct other business. The wooden structures left in the terrain have rotted over the decades, but the reinforced concrete bunkers, accommodation caves excavated in rock and anti-tank stones are well preserved.