Kajaani was one of the cities founded on 6 March 1651 by the
Swedish Governor General of Finland,
Per Brahe. At that time, the Kainuu region—as wood country—was an important producer of
tar derived from pine, and the tar trade was its major industry. In 1653–4 the district court sessions of Kajaani and
Sotkamo were responsible for authorizing a road to be built between
Säräisniemi and
Raahe, improving communications in the region. During the
Greater Wrath in the 18th century,
Kajaani Castle was forced to surrender to
Russian forces. The Russians blew the castle up in March 1716, and it has been in ruins ever since. There is a monument on the east side of the river marking where the spot where Lieutenant
Jakob Henrik Zidén and Major-General
Mikhail Petrovich Dolgorukov fell. In early 1833, medical doctor
Elias Lönnrot, best known for compiling the
Kalevala, the national epic of Finland, was appointed district physician in Kajaani and was assigned to assist in dealing with the
typhoid and
cholera epidemic which was raging during the 1830s. The disease was difficult to treat and he soon fell ill himself with typhus at the end of February 1833 but recovered. Kajaani was severely affected by the
famine in 1867–1868 which devastated much of Finland, but the town gradually recovered and by the end of the century had grown to more than 1200 inhabitants. Kajaani Town Hall was built in 1831, the former City Library in 1830, Kainuu's first elementary school in 1883, and Kajaani Church in 1896 as it grew into a notable settlement. The paper industry took off in Kajaani in the early 20th century in particular. Kajaani Paper Mill was built in 1907 and was run by the firm Kajaani Oy, which had a capital of FMK 5,000,000 (£137,615) in 1948. Kajaani Oy was eventually acquired by
Valmet in 1983, and the subsidiary Kajaani Electronics was formed. Ämmäkoski power plant was built on the river in 1917 by the Kajaani Lumber Company, and underwent alterations under architect
Eino Pitkänen in the 1940s. The city's grew in the 1960s to 14,600 inhabitants. Industrial development in the 1970s, and the merger of the separate rural municipality of Kajaani,
Kajaanin maalaiskunta, and the city in 1977 saw the population jump to 34,574 by 1980.
Vuolijoki was consolidated with Kajaani at the beginning of 2007. In 2012, an oil spill occurred in Kajaani. 110,000 liters of oily water leaked into a river that eventually flowed into the
Oulujärvi lake. ==Geography==