Holstein , (Lat. Holsatia), a former duchy of Denmark, and a state of the Germanic confederation, now part of Schleswig-Holstein, a province of Prussia. Of the history of Hol-stein until its union with Schleswig little is known. It is probable that the great migration of the Cimbri extended as far north as Hol-stein. It is known that Tiberius Caesar penetrated in the following century to the mouth of the Elbe. Tacitus seems to indicate that the seven small German tribes which worshipped the goddess Hertha inhabited the coasts of the Baltic as far as Mecklenburg and Schleswig. Of the names of these tribes, that of the Angles exists in the county of Angeln in Schleswig, and that of the Varini in the towns of Warnow and Warnemunde, in Mecklenburg; all the other names disappear in the consolidation of tribes under the name of Saxons, who are mentioned for the first time by the geographer Ptolemy. (See Saxons.) Angles, Saxons, Jutlanders, and Frisians appear together in the great emigration to Britain during the 5th century.

The Saxons in Holstein were subsequently designated as North Albingians (from Albis, Elbe), and the country was known during the middle ages as North Albingia, or Saxonia Transalbiana. They were subjugated by Charlemagne, who obtained in 811, by a treaty with Hemming, king of the Danes, the whole of Holstein as far as the Eider. His son Louis le Debonnaire founded in 834 the archbishopric of Hamburg, and gave it to Ansgar, the apostle of the north; but in 854 it was consolidated with the bishopric of Bremen. Christian civilization made however little progress in Holstein. The country was for many years harassed by Danish invaders, until Henry I. of Germany succeeded in restoring the ancient boundary between the Eider and the Schlei (934). Conrad II. ceded the territory between the two rivers to the Danish king Canute the Great in 1027, and the Eider remained from that time the northern line of de-markation. Holstein continued to bo part of the duchy of Saxony, and to be ruled by Saxon vice counts, until Duke (subsequently Emperor) Lothaire invested with it in 1106 Count Adolphus I. of Schauenburg. Adolphus II. (died in 1164) conquered Wagria, and Adolphus III. Dit-marsh; but the latter was taken prisoner by the Danes, and was compelled to cede Holstein to Waldemar II. Adolphus IV. reconquered it in 1225, and divided it between his two sons.

After their death arose five lines, of which the line Segeberg became extinct in 1308, Kiel in 1321, Plon in 1390, and Rendsburg in 1459. The Schauenburg line, which continued till 1640, possessed only part of Stomarn, the so-called domain of Pinneberg. Mechthild, daughter of Adolphus IV., married in 1237 Duke Abel of Schleswig, who was subsequently king of Denmark (1250-'52). The Danish crown fell after his death to another house, and his heirs were engaged in numerous conflicts for the possession of the duchy of Schleswig, and received great assistance from their relatives, the counts of Holstein. Denmark fell into anarchy, and Gerhard, of the Rendsburg line, ruled it from 1334 to 1340, and obtained Schleswig as a hereditary fief. His sons were not able to retain the regal power, and Denmark was reconstructed by Waldemar IV. Some portions of Schleswig remained the property of the counts of Holstein, who took possession of the whole duchy in 1375, at the death of Duke Henry, the last descendant of Abel, and obtained it in August, 1386, by treaty at Nyborg in Funen, as a hereditary fief, and Gerhard VI., of the Rendsburg line, was invested with it.

The history of Holstein from this time is included in that of Schleswig. (See Schleswig-Holstein.)