SCHLESWIG-HOLSTEIN. – Former duchy, ceded by Emperor Conrad II to Denmark in 1035 and ruled under the title of Duke by members of the Danish royal house; passed by inheritance in 1386 to the Counts of Holstein-Schauenburg; returned, after their extinction, to Denmark in 1459; became a province of Prussia in 1867.
The first missionaries were St Willibrord and Atrebanus, who died a martyr in 780 during the Saxon rebellion. Under Louis the Pious, Ebbo, archbishop of Reims, and St Ansgar, companion of King Harold of Denmark, who had been converted to Christianity in 826, attempted another mission. Due to the incursions of the Normans and the Wends, everything was again destroyed.
Under Henry I the Margraviate on the Eider was reconstituted, thus beginning a new missionary era. The archbishop of Bremen, Adaldag, founded in 948 the diocese of S. and those of Ribe and Aarhus in Denmark. Under the son of Harold, Sweyn Forkbeard, the Viking, who returned in 985, the diocese of Aarhus was suppressed and the bishops of Ribe and S. were expelled. In the last years of his life Sweyn Forkbeard became a Christian. His son Canute the Great spread Christianity throughout his entire kingdom (Denmark, England, Norway). When Canute also became Margrave of S., which until then had been part of the ecclesiastical province of Bremen-Hamburg, it passed to the Danish province of Lund, erected in 1104, to which it remained united until its suppression by Christian III of Denmark. The last Catholic bishop of S., Godschalk von Ahlefeld (1527–41), was unable to overcome the policy of the kings of Denmark, who were inclined toward the Reformation. In 1536 Christian III proclaimed Lutheranism the state religion and forbade the practice of the Catholic faith. After Godschalk’s death, Tilemann von Hussen became the first Lutheran bishop of S. In 1542 the ecclesiastical regulation of S.-H., identical to that of Denmark in 1537, was proclaimed the fundamental law of the state. Only at the beginning of the 17th century were some Catholic communities able to form. From 12 November 1669 the territory belonged to the newly erected Apostolic Vicariate of the Nordic Missions. On 29 July 1868 the Apostolic Prefecture of S.-H. was erected and placed under the provincial bishop of Osnabrück. After the Concordat with Prussia of 14 June 1929, the Apostolic Prefecture of S.-H. was incorporated into the diocese of Osnabrück by the constitution Pastoralis Officii Nostri of 13 August 1930.