​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 Christiania 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.