Sverresborg Sverresborg ( Norwegian : " Sverresborg i Trondheim " ) or Sverre Sigurdsson ' s castle ( also named Zion after King David ’ s castle in Jerusalem ) was a fortification built in the medieval city of Nidaros ( later Trondheim ) by Sverre Sigurdsson . It is now known as an open air museum for the region of Trøndelag , comprising the counties of Sør - Trøndelag and Nord - Trøndelag . Location . Defense of the city and the location of Sverresborg was based on three key topographical features : The Heklungs War . In 1177 , Sverre Sigurdsson , who was king of Norway from 1184 - 1202 , led the rebel Birkebeiner s to Trøndelag where in June , Sverre was hailed as king at Øretinget , the Thing ( assembly ) for Trøndelag . This was an important symbolic event , since traditionally new Norwegian kings were chosen there . After this , the Birkebeins moved south and wintered in Østerdalen . The next spring , the Birkebeins went back to Trøndelag , attacking the city of Nidaros ( now Trondheim ) . Defeated , they fled south until they met and beat reigning King Magnus ’ army in Ringerike . Encouraged , the Birkebeins moved north to Trøndelag again and remained in Nidaros during the winter of 1178 . In the spring of 1179 , Magnus arrived with his army . The two armies met on June 19 in the ( " Slaget på Kalvskinnet " ) and the battle was a clear victory for Sverre , securing his grip on Trøndelag . Magnus Erlingsson again attacked Trøndelag in spring 1180 . Sverre held Trøndelag from Nidaros , which was then protected by a wooden palisades extending from the river to the fjord across the neck of the peninsula connecting the town to the mainland . In the ( " Slaget på Ilevollene " ) , just outside of Nidaros , the Heklungs were again defeated . The two forces met again in 1181 in the ( " Slaget i Bergen 1181 " ) which resulted in a minor victory for Sverre . But Magnus exploited Sverre ’ s absence from Trøndelag when in November he raided and burned the Birkebeiner fleet there . Sverre was forced to return or risk losing his one secure foothold . During summer 1182 , Magnus made an attempt to take Nidaros by siege , but was repulsed with grave losses when the Birkebeins launched a surprise night attack . Castle construction . In the winter of 1182 / 1183 Sverre initiated construction of Sverresborg ( one of the earliest Norwegian fortresses ) to provide him a more secure and more easily defended base from which to work . The location selected was easily fortified , hard to approach , and could be defended by a small force . The stone for the fortification was available only 0 . 6 km away in the quarry which had been used for construction the cathedral at Nidaros . Since the Archbishop of Nidaros , who had aligned with King Magnus , was in exile in England from 1180 to 1183 , the stonemasons were also available . Work proceeded quickly , and Sverre , along with a detachment of his men , moved out to the castle during Lent in 1183 . The sea Battle of Fimreite in 1184 proved to be final struggle between the Birkebeins and the ; King Magnus drowned . King Sverre , after a six years of struggle , became the uncontested king of Norway . But the peace was not to last for long . The Bagler war . In 1188 the town of Nidaros , which had been vacated by King Sverre ’ s men , was attacked . His opposition stormed into the city and a bloodbath followed . The wooden fortress was torn down and the castle burnt and left in ruins . It is not known precisely when it was restored , but the Sverresaga indicates the castle had been restored by 1197 . He died in Bergen on 8 March 1202 . Sverresborg is last mentioned in the time of King Sverre ’ s paternal grandson , King Haakon Haakonson in 1263 , when he allowed the walls of Sverresborg to be broken down . Sverresborg Trøndelag Folk Museum . In 1914 the area surrounding the ruins of King Sverre ' s medieval castle was appropriated for the site of the new open - air museum . The castle ruins are today the center of the Trøndelag Folk Museum . The museum had started in 1909 , when a group of enthusiasts decided to gather buildings and objects characteristic of the area for purposes of preservation . The area around the fortress ruins was set aside for purposes of building a museum and the collection has grown steadily since then . Sverresborg Trøndelag Folk Museum is one of the largest cultural history museums in Norway . There are more than 60 buildings on the site now , covering a broad ethnological range .