🇮🇪 Ireland · Earthwork
Grianan of Aileach
Iron Age to Early Medieval (c.1000 BCE–1100 CE) · Iron Age Gaelic → Early Medieval Uí Néill
Donegal hilltop royal cashel (23.5 m diameter) on Greenan Mountain — northern Uí Néill kingship inauguration fort.
🇮🇪 Ireland · Earthwork
Dún Aonghasa
Late Bronze Age to Early Medieval (c.1100 BCE–800 CE) · Atlantic Iron Age / Early Medieval Gaelic
Cliff-edge triple stone fort on Inishmore (6 ha) with massive chevaux-de-frise of jagged limestone — Ireland's most dramatic hillfort.
🇮🇪 Ireland · Earthwork
Cahercommaun Triple Ringfort
Early Medieval (8th–14th century CE) over Late Neolithic traces · Gaelic Early Medieval (Eoghanacht / Dalcassian)
Triple-walled Burren cashel on cliff spur above Carran — Early Medieval high-status ringfort with 13 house platforms.
🇸🇪 Sweden · Earthwork
Eketorp Ringfort — Öland
Iron Age to Medieval (c.400–1300 CE) · Scandinavian Migration/Vendel and Medieval Gotlandic–Swedish
Eketorp, on southeastern Öland's Stora Alvaret limestone plain, is the only fully excavated of Öland's 19 Iron Age ringforts, a concentric limestone-walled fortress 70 m diameter with 53…
🇩🇰 Denmark · Hillfort
Trelleborg Viking Ringfort (Slagelse)
Viking Age (c.980–1000 CE, Harald Bluetooth) · Danish Viking Age
Archetypal Viking ring fortress west of Slagelse on Zealand, 136.5 m diameter circular earthwork with four cardinal gates, internal quadrants with 16 longhouses and outer bailey, built c.980 under…