The National Fortifications Heritage (Norwegian: Nasjonale festningsverk) is a division with the Norwegian Defence Estates Agency responsible for sixteen military fortifications in Norway designated as heritage sites. The agency is responsible for conserving the character and history of the sites, while facilitating their use for culture, business and experiences. The list consists of ten fortresses, four smaller forts and two networks of border fortifications. Three fortresses, Akershus, Bergenshus and Vardøhus, date from the Middle Ages. Five installations date from the union with Denmark and five were built either union with Sweden or following the dissolution, as a defense against a Swedish invasion. Three forts, Austrått, Møvik and Trondenes, were built by the German Wehrmacht during