Russian Fortification Works in Finland in 1915–1917
Fearing a German landing, the Russians began constructing fortifications in Finland. Between 1915 and 1917, a deep defensive zone was constructed on the mainland side of Helsinki, curving around the city in three concentric rings. The outermost ring of fortifications was located 7–8 kilometres from Helsinki. The fortifications consisted of concrete firing positions, combat and communication trenches, personnel and storage shelters, signal centres, and power stations. They were constructed mainly by excavating into bedrock. In 1915, fortification activities were also expanded inland in case the Germans landed on the coast of Ostrobothnia and advanced from there towards St Petersburg.
As Finland no longer had a national army, the soldiers stationed in Finland were Russian. Their number rose to as many as 100,000 men. The fortification works were directed by Russian engineer and sapper officers. Labour for the fortifications was brought from Russia and even from China, but Finnish civilians also participated in the work. In total, approximately 30,000 Finns took part in the fortification works.
The remains of many fortifications dating from the First World War can still be seen in various parts of Finland.