Fredriksten is a fortress in the city of Halden in Norway.

This Fortresses was constructed ny Denmark-Norway in the 17th century as a replacement for the border fortress at Bohus, which had been lost when the province of Bohuslän was ceded to Sweden by the terms of the Treaty of Roskilde in 1658. The fortress was named after King Fredrik III of Denmark and Norway, and the town of Halden was also originally named after him, having been known as Fredrikshald between 1665 and 1928.

At the close of the Northern War Charles X, having negotiated the Treaty of Roskilde in bad faith, invested Copenhagen in August 1658. Under his orders, in September the new Swedish governor of Bohuslän invaded Norway with 1,500 men and attempted to invest Halden. The inhabitants put up a vigorous defense and the Swedish forces retreated back to Bohuslän.

Five months later in February 1659 the Swedes again attacked. Since their first attack, the garrison had been strengthened. Under the leadership of Tønne Huitfeldt the Norwegian forces again repulsed the Swedish forces. Concurrently, Huitfeldt began construction of fortifications. Cretzenstein, later to be renamed Fredriksten, was the citadel of the new fortification system.