As a successful attack into the centre of the country could split it in half, the Norwegian general staff in February 1906 suggested the construction of a blocking fort in the Stjørdalen valley.

[5] The fort was built on, and named after, Ingstadkleiva — a 215-metre (705 ft) high forested hill south of the Stjørdalselva river, about 3 kilometres (1.9 mi) from the village of Hegra.

To the east, north, and north-west the terrain slopes down towards the Stjørdalen valley and is dominated by the fort, while the south front is hilly and at a higher altitude than the Ingstadskleiva.

Ingstadkleiva Fort has an excellent command of the Stjørdalen valley to the north and east, but to the west the view is blocked by the Grøthammeren and Hammeren hills, both about 300-metre (980 ft) high.

[6] The fortifications themselves consisted of 300 metres (980 ft) of halls and tunnels dynamited into the mountain at Ingstadkleiva, as well as trench systems and gun positions excavated from the rock with explosives.

[14] In late 1939, Finnish soldiers of the independent Lapland Group who had crossed the Norwegian border into Finnmark escaping the fighting in the Petsamo district in northern Finland were interned at Ingstadkleiva Fort.

After the end of the Second World War, Hegra Fortress was returned to Norwegian control and is today used as a museum with exhibitions detailing the fort's history with an emphasis on the 1940 siege.