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:
 
871-1871 
 Maa Byen som paa Tunet staar, faa blomstre nye Tusind-aar 
 
 871 - 1871
May the Town Which Stands on This Site Prosper for Another Thousand Years
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:
 
871-1871 
 Maa Byen som paa Tunet staar, faa blomstre nye Tusind-aar 
 
 871 - 1871
May the Town Which Stands on This Site Prosper for Another Thousand Years
Tønsberg Fortress