🇵🇱 Poland · Buried city
Jomsborg – Legendary Viking Harbour Fortress of the Jomsvikings
Viking Age (960–1043 CE) · Norse Jomsviking / Slavic (hypothesized)
Jomsviking fortress harbour c. 960 — saga stone arch over Dziwna channel for 30 ships; 90 m Srebrna Góra earthwork proved natural dune (hypothetical).