​TÖNSBERG, a fortified seaport of Norway, in Jarlsberg- Laurvik amt (county), situated on a bay on the south coast, near the entrance to Christiania Fjord, 72 m. S. by W. of Christi- ania on the Skien railway. Pop. (1900), 8620. It is one of the most ancient towns in Norway. It is the headquarters of a sealing and whaling fleet. The principal industries are refineries for preparing whale and seal oil and saw-mills. An interesting collection of antiquities and whaling implements is preserved in the Slotstaarn on Castle Hill.