The construction of the fortress

At the Peace of Roskilde in 1658, Bohuslän and thus Marstrand became Swedish. The town had long been an important trading post. As the harbor rarely freezes over, part of the West Swedish fleet was based here. To defend Marstrand, Carl X Gustav decided to build a fortress on the island’s highest peak. First, a square tower and walls were built around a small courtyard. In the 1680s, the fortress was strengthened by making the tower round and higher, and by raising the walls. In the early 18th century, the ramparts enclosing the large courtyard were completed. During the 18th and 19th centuries, the outer parts were built. In 1860, the fortress was reported to be completed.

Prisoners at Carlsten

Hauling stone to build the fortress was hard work. To get enough workers, a new punishment was introduced into Swedish law: ‘Marstrand labor’. Criminals were brought in from all over the country to be part of the workforce. They were murderers, grand thieves, counterfeiters and rapists, but also simpler criminals such as petty thieves and vagrants. Sentences ranged from a few years to life imprisonment.

To prevent escapes, prisoners were fitted with a two-kilogram iron ball attached with a chain around one ankle. Difficult and escape-prone prisoners could be made to wear an ‘iron crown’, a shackle that could weigh up to 36 kilograms. The hard work and poor living conditions meant that the mortality rate was high. In some winters, up to 20% of prisoners died. Marstrand labor was abolished in 1854 and most prisoners were then moved to Gothenburg.