Baltic Noble Corporations of Courland, Livonia, Estonia, and Oesel (Ösel) were medieval fiefdoms formed by German nobles in the 13th century under vassalage to the Teutonic Knights and Denmark in modern Latvia and Estonia. The territories continued to have semi-autonomous status from 16th to early 20th century under Swedish and Russian rule. The four knighthoods are united in the "Verband der Balischen Ritterschaften."