Columbia subject headings:
Germany--History--843-1273.
Germany--History--To 843.
Obodrites--History.
Harvard subject headings:
Germany--History--843-1273.
Germany--History--To 843.
Obodrites--History.
Princeton subject headings:
Polabian Slavs--History.
Slavs, Western--History.
Slavs--Germany (East)--History.