Bohus Fortress (also known as Baahus or Båhus, originally: Bágahús) lies along the old Norwegian–Swedish border in Kungälv, Bohuslän, Sweden, north east from Hisingen where the Göta river splits into two branches ( north of Gothenburg). It commands the surrounding area from a cliff high, with the river forming a natural moat around it. Initial construction The construction of Bohus Fortress (, ) began in 1308 under King Haakon V Magnuson, king of Norway from 1299 to 1319. Håkon V also initiated construction of Norwegian fortresses at Akershus and Vardøhus as part of a broader defensive policy. At the time Bohuslän (Båhuslen) was Norwegian territory and served as the main Norwegian defence against Sweden, along the coast as well as the strong point for the Bohuslän region from 1308 to 1658. Medieval castle According to architect Guthorm Kavli: Fortress The fortress was attacked or besieged 14 times, but was never captured. During the Northern Seven Years' War, in 1563–1570, it was seriously damaged. This occurred in 1566, when Swedish forces successfully stormed the 'Red Tower' in the northeast of the fortress. Two men from the garrison volunteered to detonate the tower's magazine, causing a massive explosion (the "Bohus Bang") which killed hundreds of Swedish soldiers and thwarted the attack. As a reward the family of one of the volunteers received a piece of land which is still owned by his descendants. The Norwegians rebuilt the fortress of stone and brick, and reinforced it substantially. The reconstruction immediately after the war was directed by Hans Paaske (Påske) from the Netherlands. On 1 January 1590 James VI of Scotland and his wife Anne of Denmark came to Bohus. They gave Henrik Gyldenstierne, Captain of Bohus, a ring and a gold chain worth 3,000 Danish dalers. In 1593–1604, similar to the construction then undertaken at Akershus in Oslo, Bohus was upgraded to a bastion fortress. A new outer fortification was raised. This construction was one of the early works of Hans van Steenwinckel, also from the Netherlands, who later became noted for his Dutch Renaissance style design in Denmark. As Swedish invasions continuously threatened Norwegian Båhuslen during this time period, the improvement of the fortifications went on for years. For example, starting in the summer of 1651 and until the autumn of 1652, the Dutch engineer Isaac van Geelkerck supervised the construction of two corner towers along the south façade and a new