Umbrella term for fortifications that were either purposely constructed in the water or that were once terrestrial and became inundated as a result of sea-level change.
Part of pile defence structure at the site Raasepori of castle in Finland. Photo: Sallamaria Tikkanen, Finnish Heritage Agency.
Underwater defence structure at Suomenlinna, Helsinki, Finland. Photo: Maija Huttunen.
- Guide for Archaeological Heritage in Finland: underwater defence structure: http://akp.nba.fi/wiki;vedenalainen-estevarustus