It may not be man-made but it's certainly 'megalithic', and (like in Cornwall??) may well be related to the siting of tombs like the nearby Coetan Arthur?:
The Rocking Stone (we give it a title of courtesy which has survived its peculiar property) stands on the western slope of Carn Llidi, at a short distance from the cliff, and from the road leading to St. David's Head. Its height is five feet, its extreme length and breadth each six feet six inches; and it narrows somewhat towards the bottom. A little to the east there is a point of rock which may have acted formerly as the fulcrum.
Its displacement is ascribed to the Puritans by E. Lhuyd; but we fortunately possess an account of its original state in the unknown author quoted by Browne Willis:-
About a quarter of a mile from hence is the famous Stone which they call here the Shaking-Stone, Y-maen-sigl. It is so large, that 20 Yoke of Oxen will not remove it from its Place, and yet it lieth upon a Bank; and notwithstanding its Hugeness, (they say) a Child of eight Years of Age will shake it. I never saw any Child shake it; but I can move it, tho' six Men should stand upon it, with less than the Strength of one of my Hands, so much that a Man that stands upon it, would be afraid of falling.
From p24 of 'The History and Antiquities of Saint David's' by WB Jones and EA Freeman (1856). Browne Willis was an antiquary who wrote many books in the first half of the 18th century.
You can read Jones and Freeman's book online at Google Books. It's got lots of information about the location of destroyed sites in the area, which I'm sure will be of interest to those that know the area well.
Carn Llidi is the highest point on the St David's Peninsular, and home to various forts and settlements. Two burial chambers here have pits cut into the rocks.
An aerial photograph of St David's Head. From this page you can overlay the Ordnance Survey map by clicking on the Overlay Map link on the left hand side of the screen (this is a slow process though).
I arrived at Whitesands bay carpark at gone 3 am and got a few hours tossing and turning in. (god cars are crap for sleeping in )
I started the walk over to the chamber at about 6.45 am the sun wasn't putting in an appearance today but was seen to the stoneless east of the country.
What a fantastic place for a burial chamber, just imagine if theyd'e built Stonehenge here or even just Carreg Samson, makes me quiver to think it.
The wind that had been blowing hard all night now brought in the mist off the sea, turning it into stingy face rain, Carn llidi disappeared completely which is a neat trick if you know how big it is and nature doesn't use mirrors.
I hid from the elements, no I didnt, I got closer to my ancestors and got in the chamber, using my thick hat as a cusion I sat still for a while, only noise was the wind, I closed my eyes and began to drift off.
This was the first time I ever fell asleep at a place like this, I almost remember a dream sequence, just one as I was only out for five minutes.
From here I can see a big rock just feet away, it has straight lines on it, ha nature abhors straight lines my arse, is it art or more probably fossilised sea slug tracks.
I dont think the capstone has fallen, there is a long stone on the chambers northern side that would have effectively blocked that side and the other stones here would have blocked the other gaps, also if the capstone were to be in any other position the visual impact from the south would be less and the interplay between capstone and mountain would also be lost.
Well worth the drive down and walk up, but you might not want to do it on an empty stomach with no sleep, god knows what the spirits were up to whilst I slept.
Oh what joy. (sorry just wanted to balance Dominics fieldnotes)
I came from Coetan Arthur and it was a wide and easy to follow path so theres no reason to see one without the other. On the way I saw what could have been a three stone row, probably not though. But hey why not ?
The only good thing about the gun platforms and the road to it is it makes the chambers impossible to miss.
Poor Dominic must have been on a real downer when he was here, the place was a real buzz for me, the mist had cleared somewhat revealing the fantastic views, the idea that these were childrens tombs looking over to their fathers sounds rediculous to me. More probable is the older tomb of Coetan Arthur took its focus as Carn Llidi so subsequent generations went one better and got as close to the rock as they could whilst keepking their focus on the illustrious ancestor.
Follow the track back down to the road and your just a couple hundred yards from the carpark, a brilliant and beautiful coastal ring walk.