1. A sub-megalithic site, comprising a low stone pair closely associated with a sizable earthfast natural slab, is prominent on the skyline on the north-eastern part of Skomer Island (SM 7266 0998). The pair of upright stones stand 3.25 m apart and are incorporated in the vestiges of a field boundary bank 0.8 m wide. Some 2m to the south of the western upright, and thus off-centre to the pair, is a sizable earthfast natural slab measuring approximately 2m by 2m whose front (north) edge rises 0.5 m above the ground. The slab is of note as it is isolated in clear ground and not closely matched by comparable slabs or boulders anywhere in the vicinity.

While the two upright stones to its north bear resemblance to a functional pair of gateposts in a prehistoric boundary, a number of large blocks and slabs infill the gap between them. Thus, the boundary appears to have been constructed along the line of the pre-existing stone pair, and the gap between them infilled, so as to create a continuous boundary with no entrance. Such a scenario could suggest that the stone pair were originally free-standing. Coupled with the proximity of the large earthfast slab and their highly conspicuous position on a low summit on the north of the island, where their silhouette is visible from all western and southern approaches (including from the Old Farm at the centre of island), there is the strong likelihood that the stone pair represent a megalithic, or sub-megalithic monument. The monument lies just to the north of Evans' Cairn Group 11 (1990, figure 8) and thus may be closely related to a cairnfield of unusual concentration.

There are parallels to the Coed-y-cwm chambered tomb in the Vale of Glamorgan (NPRN 275858). This is a natural slab resting on the ground surface but excavation by Glyn Daniel in 1936 recovered a polished Neolithic axe, demonstrating prehistoric use of the locale at a time contemporary with nearby chambered long cairns (RCAHMW 1976, 40).

2. Visited and surveyed using drone photogrammetry by Louise Barker and Toby Driver for the Royal Commission, 4th April 2025. 3D model available on Sketchfab: https://skfb.ly/pxP8I 

O Davis RCAHMW 16/08/11. Updated by Dr Toby Driver and Louise Barker, June 2025.

References:

Barker, L., Davis, O., Driver, T. and Johnston, R. 2012. Puffins amidst prehistory: re-interpreting the complex landscape of Skomer Island, In: Britnell, W.J. and Silvester, R. J. (eds.), Reflections on the Past, Essays in Honour of Frances Lynch. Cambrian Archaeological Association. Pp. 280-302.

RCAHMW 1976. An Inventory of the Ancient Monuments in Glamorgan. Volume 1: Pre-Norman. Part 1: The Stone and Bronze Ages. HMSO.