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Tresilian Bay Anti-invasion Defences is a reinforced concrete pillbox constructed during the Second World War as part of Britain's coastal defence network against potential invasion. Located on the Welsh coast, the structure exemplifies the rapid militarisation of vulnerable shorelines undertaken after 1940, when invasion threat was most acute. The pillbox's robust design and positioning reflect strategic assessment of this particular stretch of coastline as a potential landing site.
The monument sits on bedrock composed of Mesozoic sedimentary rocks formed during the Late Triassic period, geological foundations laid down over 200 million years before the structure's construction. This stable substrate provided suitable ground for the pillbox's foundation, though the coastal setting exposed the structure to both military considerations and the weathering effects of the marine environment. The surrounding bay's geography would have influenced its tactical placement within the wider defensive scheme.
The pillbox is protected as a scheduled monument by Cadw, the Welsh heritage organisation, under reference GM617. This designation reflects the structure's importance as material evidence of wartime defensive preparations and mid-twentieth-century military engineering. Such pillboxes remain significant historical documents, recording both the perceived vulnerabilities of the British coast and the rapid industrial response to existential threat during the Second World War.
Tresilian Bay Anti-invasion Defences is a scheduled monument protected by Cadw under reference GM617. View the official record →
Tresilian Bay Anti-invasion Defences is a reinforced concrete pillbox constructed during the Second World War as part of Britain's coastal defence network against potential invasion. It is designated a Scheduled Ancient Monument by Cadw under reference GM617.
Tresilian Bay Anti-invasion Defences dates from the modern period, and is classified as a pillbox. It is one of over 32,000 scheduled monuments protected across the UK.
Tresilian Bay Anti-invasion Defences 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 GM617.
Several scheduled monuments lie within 10 km, including Castle Ditches Camp (1 km), St Donat's Churchyard Cross (1.6 km), Llantwit Major Monastic Settlement (Site of) (1.8 km).
This page is just one thread. A full Aubrey report pulls together 13 strands of Tresilian Bay Anti-invasion Defences'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.
Tresilian Bay Anti-invasion Defences stands on Mesozoic sedimentary rocks, bedrock that formed in the Late Triassic. The rock here is sedimentary rocks.