Stockholm's permanent defence

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Stockholm’s permanent defence was a network of fortifications built around and near the city to protect it from sea, land, and air threats. The story stretches over about 700 years, from medieval walls to Cold War weapons.

Medieval beginnings and early fortifications
- The oldest installations date from the late 13th and early 14th centuries, when Stockholm grew up around Stadsholmen and the Tre Kronor Castle. The inner city wall and towers formed a protective heart for the town.
- Over time, as the city expanded, new outer walls were added in the 15th and 16th centuries. Little remains above ground today, but a few foundations and towers survive, including the Lejon Tower’s foundation visible today in a hotel.
- The northern city wall remnants are preserved in the Museum of Medieval Stockholm, and other medieval fortifications, like walls and towers on Riddarholmen, are still visible in some form.

Fortresses and coastal defences in the early modern era
- In the 16th century, Vaxholm Fortress began to guard the approach to Stockholm, and the capital’s protection became part of a broader national defence strategy.
- The 17th century saw the war council and fortification architect Erik Dahlbergh lead many improvements. He and his team built sconces and batteries along the coast to defend sea routes to and from Stockholm and to protect land passages around Södermalm.
- Along the Stockholm archipelago, sconces and fortifications were built at various points from the 1620s onward. These works faced funding problems and were often accelerated or halted by money shortages. Some were demolished or left to decay after wars.

19th century shift and private initiatives
- In the 1800s the big question became how to defend Stockholm from eastern threats, but big fortification projects largely stalled due to cost.
- A new defence concept emerged toward the end of the 19th century: central defence gave way to border and coastal defence. The city received some upgrades, including a fortress at Oxdjupet (Oskar-Fredriksborg) to guard the entrance to Stockholm.
- Private initiatives helped fund new works around Stockholm. The Palmqvist Foundation and the Society for Stockholm’s Permanent Defence gathered money from wealthy citizens to build fortifications around the capital, known as the Korvlinjen or the Sausage Line. These were mostly underground infantry and machine-gun emplacements with low, curved roofs that blended into the landscape.

Sea and air defence in the 20th century
- Stockholm’s coastal defences included the Vaxholm Line and later the Vaxholm Outer Defence Line, protecting important straits and fairways.
- After World War I, air defence began to develop. Stockholm built anti-aircraft positions and improved archipelago defences (the Havsbandslinjen) between 1936 and 1945.
- In 1943–1944 Stockholm prepared for possible aerial and ground attacks. A core defence line ran through central districts (like Norrmalm, Östermalm, Kungsholmen, and Södermalm), with tank obstacles and fixed anti-aircraft positions. About fifty anti-aircraft positions and several searchlights existed in 1944.
- The Soviet air raid on February 28, 1944 demonstrated the vulnerability of even well-defended cities. Only one battery fired live rounds; most missiles and guns were not used, and the raid caused limited damage but spurred political and military responses.

Postwar changes and civilian shelters
- After World War II, anti-aircraft defences were dismantled or stored away, though many concrete barriers and dragon’s teeth remained in the landscape into the 1950s.
- Sweden built a vast network of civilian nuclear-safety shelters in Stockholm County—around 14,500 shelters, providing about 1.7 million places. Some large shelters near the city center were repurposed as parking garages later on.
- The navy moved its ships to the Muskö Naval Base in the late 1960s, and many training areas around the Stockholm archipelago were reduced or handed over to civilian use. Some areas remained active for defense training into the 2000s.

The ERSTA era and the end of permanent defence
- In the 1960s Sweden adopted a new approach to defence, focusing on border and coastal defence with updated technology.
- The ERSTA system, built along the Baltic coast from 1973 to 1983, consisted of six top-secret, highly advanced artillery batteries designed to defend against a Soviet attack.
- After the Defence Act of 2000, all ERSTA batteries were dismantled except for the Landsort battery (gun no. 3), which was preserved as a public memorial to Sweden’s Cold War defence effort.
- The ERSTA system marks the end of the era of permanent defence in Sweden.

Remnants today
- Very few medieval and early modern fortifications survive in their original form, but some features endure as museums or protected sites. A small piece of the northern city wall, Birger Jarls torn on Riddarholmen, and various sconces and batteries can still be seen or visited. Many other remains are overgrown, private, or have been removed over the years.
- The story of Stockholm’s permanent defence shows how the city tried to protect itself for centuries, often with limited funds, evolving threats, and changing military ideas.