Location: MarstrandmMap
Constructed: 1658
Carlsten Fortress (Swedish: Carlstens fästning) is a historic stone coastal defense installation located on the highest point of Marstrand Island, in Kungälv Municipality, Västra Götaland County, on the west coast of Sweden. Situated at coordinates 57°53′10″N 11°34′42″E, approximately 45 kilometers northwest of Gothenburg, it overlooks the Kattegat Sea and the harbor town of Marstrand, which has been a key trading post due to its ice-free port. Built starting in 1658 by order of King Carl X Gustav (Karl X Gustav) following the Treaty of Roskilde, which ceded the Bohuslän province from Denmark to Sweden, the fortress was named after the king and designed to safeguard the newly acquired territory and its strategic harbor. Spanning over 200 years of construction and expansion, it evolved from a simple tower into a massive complex with ramparts, bastions, and barracks, serving dual roles as a military stronghold and state prison. Decommissioned in 1882, Carlsten is now Sweden's largest coastal fortress and a major tourist attraction, offering guided tours, themed events, and overnight stays in historic buildings. Recognized for its imposing granite architecture and panoramic sea views, it draws visitors interested in Swedish military history, with an average Tripadvisor rating of 4.5/5 from over 200 reviews praising its well-preserved state and engaging experiences.
The fortress's history is deeply tied to the geopolitical shifts of
the 17th century. Following the Treaty of Roskilde in 1658, which ended
the Dano-Swedish War and transferred Bohuslän (including Marstrand) from
Denmark to Sweden, King Carl X Gustav recognized the strategic value of
Marstrand's natural harbor—one of the few ice-free ports in the
region—and ordered the construction of a permanent defense to counter
potential Danish reconquests. Initial work began in 1658 under the
supervision of commander Johan Wärnschöld, starting with a makeshift
wooden fortification (Wahlen skans) on the site of a former windmill
hill, which successfully repelled a Norwegian attack in 1659. By 1666, a
more durable square stone tower (initially called Karlsten) was erected,
equipped with a roof battery, marking the transition to permanent
structures.
Expansion accelerated in the 1680s under designs by Erik
Dahlbergh, with the square tower converted into a taller, round
structure by 1689, incorporating brick redoubts and high walls. The
ramparts enclosing the large courtyard were completed in the early 18th
century, and outer fortifications were added throughout the 18th and
19th centuries, with the fortress declared fully complete in 1860. Much
of the labor was provided by prisoners under the "Marstrand labor"
punishment, introduced specifically for this project, where convicts
(from murderers to petty thieves) hauled granite and built the walls,
often under brutal conditions leading to high mortality rates.
Militarily, Carlsten was besieged twice: first in 1677 during the
Scanian War, when Danish-Norwegian forces under Ulrik Frederik
Gyldenløve captured it after an assault on Marstrand, holding it briefly
before Sweden regained control through negotiations; and again in 1719
during the Great Northern War, when Norwegian Vice-Admiral Peter
Tordenskjold (Tordenskiold) bombarded and seized it, only for it to be
returned via treaties. Despite these falls, the fortress was never taken
by direct storming of its walls. It served as a base for the Swedish
Navy and a prison until the mid-19th century, with notable inmates
including the cross-dressing thief Lasse-Maja (Lars Larsson Molin),
imprisoned from 1813 to 1839 and later pardoned by King Karl XIV Johan
after serving as a cook, and Metta Fock, a rare female prisoner held
from 1806 to 1809. The prison system was abolished in 1854, and the
fortress was dismantled as a military installation in 1882, remaining in
limited military use until the early 1990s.
Carlsten Fortress is a classic example of 17th-19th century European
coastal artillery architecture, built primarily from local granite and
brick to withstand sieges and naval bombardments. The core structure
revolves around a central round tower—the highest and most iconic
element—originally square (built 1666-1673) but redesigned in the 1680s
into a multi-story cylindrical form with a roof battery for cannons.
This tower, incorporating the earlier square base, is surrounded by high
curtain walls and a brick redoubt with four small ravelins (triangular
outworks) for defensive firing angles.
The layout forms a large
enclosed courtyard, fortified by ramparts completed in the early 18th
century, with outer bastions and barracks added over time. Key
structural features include the Donjon (a fortified tower-like building
used for soldier accommodations) and Kommendantshuset (commander's
house), both from the 18th-19th centuries, now repurposed for overnight
stays. The fortress's rugged, imposing design—built directly into the
rocky island terrain—includes gun emplacements, underground passages,
and high walls that provided 360-degree defense, particularly against
naval threats from the Kattegat. Materials like granite ensured
durability, while prisoner labor allowed for extensive expansions,
resulting in a complex that covers the island's summit and integrates
with its natural cliffs.
Carlsten Fortress's main draw is its immersive historical
experiences, blending military heritage with interactive events.
Guided tours, available daily in Swedish (with English options
seasonally), explore the tower, ramparts, and prison cells,
highlighting stories of sieges, prisoners, and daily life—lasting
about 1 hour and praised for their engaging narratives. Themed
events include the "Carlsten Murder Mystery," where participants
solve a suspenseful case in the historic setting, combining history
with interactive theater. Overnight stays at Soldathotellet in the
Donjon and Kommendantshuset offer a unique "soldier's life"
experience in charming, historic rooms.
Panoramic views from the
ramparts overlook Marstrand's colorful wooden houses, the harbor,
and sailing events, making it a photographer's haven. Other features
include exhibits on prisoner labor (e.g., displays of iron shackles
and the "iron crown" weighing up to 36 kg) and naval history, plus
seasonal dinners and cultural programs. The fortress's location on
car-free Marstrandsön enhances its allure, with a short ferry ride
adding to the adventure.
Carlsten Fortress is open daily year-round, with extended hours in
summer: typically 11:00 AM to 5:00 PM, though note closures on
Midsummer's Eve and Day (June 20-21, 2025). Admission prices are around
100-150 SEK for adults (exact figures vary; check website), including
access to the grounds and exhibits; guided tours cost extra (about
50-100 SEK). Reach the site via ferry from Koön to Marstrandsön
(2-minute crossing, frequent service), as no cars are allowed on the
island; from Gothenburg, it's a 45-minute drive or bus ride to Koön.
Tips: Book tours in advance, especially for English-language options or
events like the murder mystery. Wear comfortable shoes for the uphill
walk from the ferry (10-15 minutes) and uneven terrain; the site is
partially accessible but challenging for mobility issues due to stairs
and cobblestones. Visit in summer for optimal weather and events, or
autumn for fewer crowds; plan 1-2 hours for exploration. Combine with
Marstrand's beaches, sailing, or nearby attractions like the town
harbor. Official website: www.carlsten.se for bookings and updates.