Kajaani Castle (Finnish: Kajaanin linna, Swedish: Kajaneborg, Kajaneborgs slott, older spelling Cajanaborg) was built in the early 17th century on an islet in the Kajaani River, between the Ämmäkoski and Koivukoski rapids in Kainuu, present-day Finland. It was the last Medieval-style stone castle constructed in Sweden.

The castle experienced its peak during the tenure of Count Per Brahe the Younger from 1650s to 1670s. The town of Kajaani was founded in 1651 next to the castle, and plans were made to transform the castle into a noble residence. However, in 1681, the fief was abolished during the Great Reduction, and the castle reverted to serving as a simple administrative center for Sweden's northernmost territories. During the Great Northern War, Russian forces sieged the castle and destroyed it with explosives in 1719. Today, only its roofless ruins remain.^[1]

The castle functioned as an administrative centrum, prison, and military strongpoint. The most famous prisoner was the historian Johannes Messenius, who was forced to live in the poor conditions of the castle from 1616 to 1635. During the imprisonment period, Johannes Messenius from Uppsala University, wrote a work of fifteen parts masterpiece concerning the history of Scandinavia called Scondia Illustrata, which was published more than 60 years later, between the years in 1700–1705 in Stockholm.

The first nine part within the content of the Scondia illustrata form a chronicle called the Chronologia, which describes the history of Scandinavian people starting from times of the Genesis flood narrative until the Gustavus Adolphus reign ergo from 1611 to 1632. The remaining six volumes deal with the history of Finland and the Baltic Vendies and contain additions to the previous volumes.^[2]

Construction of Kajaani Castle began in 1604 and was completed in 1619. At first, the castle only consisted of a stone wall, two round towers, and wooden buildings in the yard inside the castle.

Count Per Brahe ordered major additional construction of the castle in the 1650s, which was completed in 1666. During this construction, many wooden structures of the castle were replaced with stone structures to form a fortress.

In 1716, during the Great Northern War, Russian forces besieged the castle for several months until it was finally forced to surrender because of lack of food, firewood, and ammunition. Shortly after this, the Russians blasted the castle, and its inhabitants were deported to Russia and imprisoned there.

In 1917 a hydro-electric plant was built at Ämmäkoski.

The first wooden bridge on top of the ruins was built in 1845. By 1937 the castle island became the foundation for a new road bridge made of concrete.

The bridge, called Linnansilta ("castle bridge"), was originally the only bridge across the Kajaani River. After the construction of later bridges, traffic across Linnansilta decreased, and there are plans to take down the bridge and give this national monument a due and proper restoration.^{[citation needed]}

• Brahe Castle
• Oulu Castle

• Kajaani Castle by the University of Oulu
• The National Board of Antiquities

• Media related to Kajaani Castle at Wikimedia Commons

64°13′45″N 027°43′58″E / 64.22917°N 27.73278°E / 64.22917; 27.73278