Castilly Henge or Plen-an-gwarry?

 

The archaeological trenches at Castilly Henge in Luxulyan, Cornwall, are now well into their third week, of the four-week excavation programme, 15 September to 10 October 2025. This collaborative effort between Historic England, the Cornwall Heritage Trust, and the Cornwall Archaeological Society aims to ground-truth the intriguing anomalies detected in the 2022 geophysical surveys, particularly the eccentric ovoid arrangement of pits in the southern interior, some of which hinted at recumbent stones. The project's blogs and social media updates emphasise community engagement, but the silence on artefacts or structures builds suspense ahead of the public open day on 11 October. https://www.cornwallheritagetrust.org/community/castilly-henge/

Labelled a Class I henge due to its ovoid form (approximately 49m north-south by 30m east-west), internal ditch, and external bank, the site's prehistoric credentials have always been tenuous. The 1962 excavations by the Cornwall Archaeological Society, directed by Charles Thomas and published in 1964, found scant evidence beyond two undiagnostic flint flakes and the monument's general resemblance to other henges.

"Apart, perhaps, from the two flint flakes, only one of which actually occurred in primary silting, there is no evidence that Castilly is a prehistoric henge at all, save from the general resemblance to Class I henges." https://cornisharchaeology.org.uk/2022/08/19/volume-3-1964/

Instead, the work revealed extensive medieval remodelling: disturbed ditch silting redeposited to create a spectator-friendly internal slope, a secondary southern entrance formed by filling a natural causeway with bank spoil, and 13th-14th century pottery sherds in key contexts. Thomas concluded that Castilly had been adapted as a plen-an-gwarry, a Cornish amphitheatre for miracle plays like Perran Round. https://st-piran.com/perranround.html

The 2022 surveys—employing vehicle-towed GPR, earth resistance, and magnetometry—reignited debate by identifying pits (c. 1.5m diameter, 0.65-1.3m deep) forming an incomplete southern arc, with rectilinear anomalies suggesting buried stones. https://historicengland.org.uk/research/results/reports/8881/CastillyHengeLuxulyanCornwall_ReportonGeophysicalSurveysFebruary2022

This has fuelled speculation of a "hidden stone circle," drawing parallels to Cornish sites like the Stripple Stones. However, as sarsen.org readers know, geophysical data can be deceptive, and Castilly's anomalies demand cautious interpretation. I remember the cautionary tale of Durrington Walls and the so-called "superhenge", where similar optimism met a sobering reality. The geophysical signals of wooden post holes had mimicked stones due to chalk backfill and compaction, and no buried megaliths were present.

Castilly's situation mirrors this closely. The 2022 GPR and earth resistance data showed high-amplitude anomalies, but magnetometry was subdued, possibly from the site's slate geology rather than stone fills. The pits' rectilinear shapes could indicate flat-lying stones—or, as at Durrington, the voids left by extracted timbers. If the ongoing trenches reveal empty sockets or postholes with prehistoric fills (e.g., charcoal for dating), it might confirm a Neolithic phase with temporary uprights, perhaps for rituals before abandonment. But if medieval material dominates, or the anomalies prove natural/geological, the henge theory falters, reinforcing Thomas's medieval amphitheatre interpretation.

Comparisons with Perran Round bolster this scepticism. That site, with its circular rampart, external ditch, and central depression (the "Devil's Spoon" for theatrical "Hell"), is a documented plen-an-gwarry with Iron Age origins but medieval primacy. Castilly's irregularities—ovoid shape, segmented ditch, secondary entrance—could similarly reflect adaptation for drama, with pits as postholes for temporary play structures rather than prehistoric settings. The 1964 sections showed no internal features in the central area, despite stripping to bedrock, suggesting any anomalies are peripheral and potentially later.

So is it a henge? with stones? I hope so, but until the results of the present excavations are revealed we just don't know. https://historicengland.org.uk/research/current/discover-and-understand/landscapes/castilly-henge-excavation/