Boden Fortress () is a modern fortress consisting of several major and minor forts and fortifications surrounding the city of Boden, Norrbotten, in northern Sweden. The fortress was originally intended to stop or delay attacks from the east or coastal assaults, which at the time of construction meant Russian attacks launched from Finland. It was primarily the expansion of the railway net in Norrland, which in turn was a consequence of the rising importance of the northern iron ore fields, that led to the increased strategic value of northern Sweden and the construction of the fortress. Although the main forts were finished in 1908, many of the supporting fortifications were not completed until the start of the First World War. Improvements were also continuously made during, and between, both World Wars. Boden Fortress is made up of five primary self-supporting forts excavated out of the bedrock in five of the mountains surrounding Boden: Degerberget, Mjösjöberget, Gammelängsberget, Södra Åberget and Rödberget. Eight fortified secondary artillery positions were constructed between the forts to give flanking support and to cover areas not in range of the main forts' artillery. In addition, 40 bunkers for infantry, along with dugouts and other fortifications, were built to cover even more terrain. During the Second World War anti-tank gun emplacements and additional bunkers and shelters were built, and tens of kilometres of dragon's teeth were placed around the fortress and the city itself. Owing to the end of the Cold War and the reduction of the threat from the Soviet Union, Boden Fortress became less important to the defence of Sweden, and began to be decommissioned. The last fort of the complex was decommissioned on 31 December 1998, and is now used as a tourist attraction. All five forts as well as some of the supporting structures have been declared historic buildings, to be preserved for the future, by the Swedish government. Background Central and peripheral defence The two dominating theories of how to use fortifications in the operational perspective during the 18th and 19th century were the central fortress system () and the peripheral fortress system (), the latter also called the cordon system. The two systems were also known as central defence and peripheral defence. The peripheral defence theory was based on building smaller fortifications in advance positions to meet the enemy at an early stage, while the central defence theory was meant to weaken