Hegra Fortress () is a small mountain fortress in the village of Hegra in the municipality of Stjørdal in Trøndelag county, Norway. Originally known as Ingstadkleiven Fort (also Ingstadkleiva Fort), it was built between 1908–1910 as a border fort as a defence against the perceived threat of a Swedish invasion. Background The intent behind Ingstadkleiva Fort was to block Swedish advances into Central Norway, as had happened repeatedly during the Swedish-Norwegian conflicts in the preceding centuries, for example the Hannibal War, Northern Wars, and Great Northern War. After the 1905 dissolution of the union between Norway and Sweden, the Norwegian military harboured continued fears of a Swedish invasion to retake Norway. 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. Ingstadkleiva was early on pointed out as a good location to block an advance from the east. Already in March that year the Minister of Defence, commanding general, and chief of the Fortress Artillery surveyed the site and agreed to the plan. In a closed meeting on 26 April 1906, the Norwegian Parliament authorized the construction of Ingstadkleiva Fort, but no funds were allocated until 12 July 1907. In May 1908, the work began on the road up to the construction site and by January 1910 the fort was ready for use. Geography The fort was built on, and named after, Ingstadkleiva — a high forested hill south of the Stjørdalselva river, about 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 high. Ingstadkleiva Fort The fort's guns came from the dismantled Ørje Fortress in Marker. The artillery was made up of flat angle guns with a range of . The fortifications themselves consisted of of halls and tunnels dynamited into the mountain at Ingstadkleiva, as well as trench systems and gun positions excavated from the rock with explosives. There are two main underground parallel tunnels of around length, with a tunnel connecting them at