- A
Viking ring fortress, Trelleborg-type fortress, or
trelleborg (pl. trelleborgs), is a type of
circular fort of a
special design,
built in Scandinavia...
- ISBNÂ 87-89531-15-9. Else Roesdahl. "Broer,
Ringborge og
Dannevirke [Bridges,
Ringcastles and Danevirke]". danmarkshistorien.dk (in Danish).
Aarhus University...