Christiansholm fortress

It was built in 1672 during the reign of Danish king Christian IV to protect the port city of Kristiansand (founded 1641) by the Danish engineer Willem Coucheron. It is a mighty squat round artillery tower surrounded by not a high bastion wall. In the old times it stood on an island, but now you can walk to the fortress along the dam, built in the second half of the 19th century.