Tønsberg Fortress (Tunsberghus festning) was a medieval fortress and castle, located in Tønsberg, Norway which was defended by the fortress for over 300 years. It includes ruins from Castrum Tunsbergis, Norway's largest castle in the 13th century, originally built by King Håkon IV, the grandson of King Sverre. History Dating in 871, Tønsberg is commonly believed to have been the oldest Norwegian town and one of the oldest recorded fortified locations in Norway. According to Snorri Sturluson, Tønsberg was founded before the Battle of Hafrsfjord under which King Harald I of Norway united Norway under his rule. Tønsberg was an important trading center and site of the Haugating, the Thing (assembly) for Vestfold and one of Norway's most important places for the proclamation of kings. In the 13th century, King Haakon Haakonson built a castle, Tunsberghus, at the location of the modern Tønsberg municipality. It was located at what was formerly one of the most important harbors in Norway. The castle was greatly expanded during the reigns of Håkon Håkonsson and Magnus Lagabøte, who added large walls, towers, residential halls and a church. The last king of a fully independent Norway, Håkon V Magnusson, died at the castle in 1319. Only a few ruins of the fortress remain today. The modern-day tower (Slottsfjellet i Tønsberg) was raised in 1888 as a memorial of the historic fortress. In 1971, local authorities improved the insulation. At that time new plaques were mounted inside the tower. On the sides are the gilded signatures of three modern Kings of Norway: Haakon VII (1 August 1906), Olav V (1 July 1958) and Harald V (9 March 1992). The plaque over the entrance reads: Chronology 871 - The commercial town of Tunsberg existed. It served as a stronghold for the Ynglings, who first came to power in Vestfold in this period. 11th century - The commercial town and fortress at Tunsberg, on the Oslofjord outdistanced Skiringssal as a trading center. 1201 - Sverre Sigurdsson, king of Norway from 1177–1202, was attacked in Oslo by combined forces from the Oppland, Viken, Telemark and Tunsberg. Although they outnumbered Sverre's forces, they were defeated by Sverre's superior tactics. One of their ablest leaders, Reidar Sendemann, took refuge in the heights of Tunsberg mountain. In September 1201, Sverre lay siege with a force of 1000 men, forcing their surrender after 5 months. Unfortunately for Sverre, he took ill in the