Tønsberg Fortress

Dated to 871, Tønsberg is commonly believed to be the oldest Norwegian town and one of the oldest recorded fortified locations in Norway. Snorri Sturluson has the town founded before the Battle of Hafrsfjord, at which Harald I united Norway under his rule. The commercial town served as a stronghold for the Ynglings, who first came to power in Vestfold in that period, and it was the site of the Haugating, the assembly for Vestfold and one of Norway's most important places for the proclamation of kings. By the 11th century the commercial town and fortress on the Oslofjord had outdistanced Skiringssal as a trading centre.

In 1201 King Sverre Sigurdsson, who had ruled since 1177, was attacked in Oslo by combined forces from the Oppland, Viken, Telemark and Tunsberg. Although they outnumbered him, they were defeated by Sverre's superior tactics, and one of their ablest leaders, Reidar Sendemann, took refuge in the heights of Tunsberg mountain. Sverre laid siege in September 1201 with a force of a thousand men and forced their surrender after five months. He fell ill during the siege and returned to Bergen, only to die later in 1202.

In the 13th century King Håkon Håkonsson, grandson of Sverre and king from 1217 to 1263, built the castle of Tunsberghus at what was then one of the most important harbours in Norway. In 1253 he constructed a castellated wall around the mountain and provided support buildings within the fortification; in the same year the fortress successfully resisted an attack by Danish forces. The castle was greatly expanded during the reigns of Håkon and of Magnus Lagabøte, who added large walls, towers, residential halls and a church, and the fortress includes ruins from Castrum Tunsbergis, Norway's largest castle in the 13th century.

Magnus Lagabøte, king from 1263 to 1280, brought his bride Ingeborg of Denmark to live in the castle in 1261. Håkon V Magnusson, king from 1299 and the last of the Haralds-ætten — the last king of a fully independent Norway — lay ill and died at Tønsberghus in 1319. In 1335 Magnus Eriksson was wedded here to Blanche of Namur, who received the castle as a gift from her husband.

After 1387, when the castles were no longer occupied by Norwegian royalty, the governors of the four chief Norwegian fortresses — Tønsberghus, Akershus, Båhus and Bergenhus — ranked among the realm's most important lords. As the Kalmar Union collapsed, Norwegian attempts to rebel were suppressed by Danish forces. In 1503 Tunsberghus was burnt down and destroyed by Swedish soldiers and disloyal local peasants.

Only a few ruins of the fortress remain. Tønsberg Maritime Club built a wooden watchtower in 1856, which burnt down in 1874, and the present tower, Slottsfjellet i Tønsberg, was raised in 1888 as a memorial of the historic fortress. Local authorities improved the insulation in 1971 and mounted new plaques inside; on its sides are the gilded signatures of three modern kings of Norway, Haakon VII on 1 August 1906, Olav V on 1 July 1958 and Harald V on 9 March 1992. The plaque over the entrance carries the dates 871–1871 and the wish "Maa Byen som paa Tunet staar, faa blomstre nye Tusind-aar" — may the town which stands on this site prosper for another thousand years.

The site is held under cultural heritage preservation in Norway. Slottsfjell Museum was established in 1939 as the Vestfold Fylkesmuseum and is now an associate of Vestfoldmuseene; its exhibitions present Vestfold's cultural history, with particular emphasis placed on whaling and shipping and on urban and rural history in Vestfold to the Second World War.