The ring castles and the contemporary Ravning Bridge over Vejle Rivertogether with minor bridges erected on Zealand (Bakkendrop bridge between Gørlev Tissø and Risby bridge by Præstø) and Lolland (over Flintinge river)differ clearly from others from the Viking Age. Unlike other ring castles from the period the ring castles which follow the Trelleborg model are constructed after a strictly geometrical plan and measured with the Roman foot. The pointed bottoms of the moats is another element borrowed from the Ancient Romans.