As indicated by archeological findings in the city, the Kristiansand area has been settled at least since 400 AD. A royal farm is known to have been situated on Oddernes as early as 800, and the first church was built around 1040. The first settlements near the modern city were located further down the river, in or near what is today the borough of Lund, and at Flekker�y, an island outside the city centre.
Kristiansand was formally founded by King Christian IV in 1641. It was created as a market town to encourage growth in a strategically significant area, providing a local economic base for construction of fortifications and population for defence of the area. The centre of Kristiansand, in layout essentially unchanged since the 17th century, is called "Kvadraturen" due to its square gridline of streets.
The city experienced its first major town fire in 1734, when large parts of the city was destroyed. Kristiansand grew into a major port during the 18th century, both due to its expanding ship building industry and its trade fleet. The city burned again in 1892. As a neutral trade port, the economy of Kristiansand thrived during World War I, but the growth stagnated due to political decisions and the Great Depression of the late 1920s and 1930s. During the attack on Norway 9 April 1940 it came to a battle between a German naval force and the Norwegian coast fortresses near Kristiansand. The city was occupied during the day and held by German forces the rest of World War II.
Kristiansand was established as a municipality 1 January 1838 (see formannskapsdistrikt). The rural municipalities of Oddernes, Randesund and Tveit were merged with Kristiansand on 1 January 1965
