Schleswig, Or Sleswick (Dan. Slesvig). I. Formerly an independent duchy governed by the king of Denmark, now the N. part of the Prussian province of Schleswig-Holstein. It is bounded N. by Jutland, from which it is partly separated by the Konge Aa, E. by the Little Belt and the Baltic, S. by Holstein, from which it is separated by the Eider river and the Schleswig-Holstein canal, and W. by the North sea; extreme length 90 m., general breadth about 40 m.; area, 3,529 sq. m.; pop. in 1871, 409,907. (See Schleswig-Holstein.) - Since the time of Charlemagne Schleswig has been a disputed possession between the Germans and the Danes. A margraviate erected here by Henry I. of Germany about 934, and reorganized by Otho the Great in 948, was yielded up to Canute the Great in 1027, when the Eider was agreed upon as the boundary between the two countries. Thenceforward Schleswig was usually bestowed upon the younger princes of the Danish reigning family. King Waldemar II. (1202-'41) invested with it his younger son Abel, whose descendants, closely allied with the counts of Holstein of the Schauenburg house, but usually hostile to the Danish kings, ruled it till 1375. During this period the foundation was laid for the union of the two territories, and in 1326 the so-called constitution of Waldemar was adopted, according to which Schleswig was never again to be united with Denmark under the same lord.
After the extinction of Abel's line, the counts of Holstein laid claim to Schleswig under several treaties, and in 1386 Gerhard VI. received it as a Danish fief. Although Holstein was a fief of the empire, the history of the two countries is from this time united.
A City Of Prussia, in the province of Schleswig-Holstein, formerly capital of the duchy of Schleswig, at the head of a shallow bay called the Schlei or Sley, about 20 m. from the Baltic, and 69 m. N. N. W of Hamburg; pop. in 1871, 13,850. It is almost surrounded by water, and is divided into three parts, the Altstadt, chiefly inhabited by fishermen, the Lollfuss, and Friedrichsburg. It has a cathedral with many monuments. Woollen goods, leather, lace, and china are made. The harbor is accessible to small vessels. Schleswig was in existence in 808, and for nearly 600 years it was an important commercial city. It declined from the gradual filling up of its harbor.