Along the Göta River, Danish, Swedish and Norwegian history is interwoven. The role of the river grew in importance during the Iron Age and thus control over it had a strategic significance. In the 1250s, the Norwegian king built a fortification on Ragnhildsholmen to protect the town of Kongahälla. In 1308, a wooden castle was built on Bagaholmen, which was named Bagahus, and later Bohus.

For more than 300 years, it expanded and was strengthened by Norwegian and Danish kings, mainly Christian IV who visited Bohus and Norway more times than all the Danish kings combined. From 1450 to 1658, Danish kings ruled over Norway. Bohus resisted hostile sieges 13 times, but during its heyday Bohuslän became a part of Sweden due to the peace treaty in Roskilde. The Renaissance castle was then emptied and given to the Swedish king.

In 1789, Gustav III ordered the fortress to be levelled to the ground, but in 1838, Carl XIV halted further destruction of the landmark.