a seaport of Norway, in Jarlsberg-Laurvik amt (county), beautifully situated on the west bank of the Christiania Fjord, opposite Moss, 38 m. by water and 66 by rail S. of Christiania. Pop. (1900) 8460. It is practically united with Karl-Johansvaern, which is defended by strong fortifications, is the headquarters of the Norwegian fleet, and possesses an arsenal and shipbuilding yards. There are also an observatory and a nautical museum.