Worlds greatest foresters. Finland - Finnish daily life Forest Academy of Korkeakoski 1939 From a series These Men Built the Mannerheim Line - the Finnish zone of frontier fortifications was designed and constructed entirely by the Finnish people. Finnish engineers began work on the line in 1937 but it was not until this summer in 1939 that the work was speeded up and completed. Then, conscious of the dangers of a weak frontier, Finnish young men and students gave up their summer holidays in order to help voluntarily in the building of tank traps and fortifications.