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Sully Island "Danish" Fort is a prehistoric hillfort located on Sully Island in Wales, protected as a Scheduled Monument by Cadw under reference GM035. The fort occupies a commanding position on bedrock composed of Triassic sandstone and conglomerate, the mixed lithologies providing a naturally defensive foundation. The interbedded Triassic rocks underlying the site would have presented both obstacles and opportunities for the hillfort's builders, whose stone fortifications were likely constructed from locally quarried material.
The fort's earthworks follow the contours of the island, exploiting its natural geography to create defensible enclosures. The sobriquet "Danish" reflects historical speculation about the site's origins, though prehistoric occupation remains the most firmly established period of use. The coastal location on an island position would have offered security against land-based threats whilst maintaining access to maritime resources.
The monument survives as substantial earthwork remains visible across the island's landscape. Its preservation within the designated area protects an important record of Iron Age or earlier defensive settlement in South Wales. The site's prominent situation and construction methods reflect the strategic importance of controlling both coastal approaches and inland routes in prehistoric South Wales.
Sully Island, "Danish" Fort is a scheduled monument protected by Cadw under reference GM035. View the official record →
Sully Island "Danish" Fort is a prehistoric hillfort located on Sully Island in Wales, protected as a Scheduled Monument by Cadw under reference GM035.
Sully Island, "Danish" Fort dates from the prehistoric period, and is classified as a hillfort. It is one of over 32,000 scheduled monuments protected across the UK.
Sully Island, "Danish" Fort is a Scheduled Ancient Monument, legally protected by Cadw — the body responsible for designating and safeguarding heritage sites in Wales. The official designation reference is GM035.
Several scheduled monuments lie within 10 km, including St Mary's Well Bay Pillbox (0.8 km), Anti-aircraft and Coastal Battery West of Lavernock Point (1.2 km), Middleton Moated Site (2.5 km).
This page is just one thread. A full Aubrey report pulls together 13 strands of Sully Island, "Danish" Fort's history, each drawn from the record and mapped to the exact spot:
Every location is different. Not every section appears for every place, only what the historical record actually holds turns up in a report.
Sully Island, "Danish" Fort stands on Triassic Rocks (Undifferentiated), bedrock that formed in the Triassic. The rock here is sandstone and conglomerate, interbedded.