SLESWICK, an ancient and considerable town of Denmark, and capital of a duchy of the same name in the province of Gottorp, with a bishop's see, secularized in 1586. Close to it is the old palace of Gottorp, formerly the ducal residence, but at present inhabited by the stadtholder or governor. This town was once much more considerable than it is at present, having suffered greatly by the wars of Germany. It is seated on the gulph of Sley, where there is a good harbour, 60 miles north-west of Lubeck, and 125 south-west of Copenhagen. E. Long. 10. 0. N. Lat. 54. 40.