I visited the gold mines two years ago on what I remember was a nice sunny day. (N.T. site) What I thought was a small valley was in fact the quarried side of the hill. An interesting place to visit in a very pretty valley.
Whilst I was there I saw a large squarish block of stone which I just assumed had been used for some reason to do with the mining.
It appears that I was actually looking at Carreg Pumsaint? If you visit the mine the stone is easy enough to spot.
I tried to buy a visitor's guide (as I always do as a keepsake) but I was told they didn't do any!
Luckily a member of staff gave me a battered old photo copied booklet one of them had made themselves! (Thank you to that person)
A curious legend connects the Five Saints with a large block of sandstone at Cynwyl Gaio called Carreg Pumpsaint. It stands upright at the foot of the hill below the Ogofau, the old Roman gold mines, and is shaped like a basalt column, with large artificial oval basin-shape hollows on its sides. It is three and a half feet high and a little over two feet in width.
The legend says that, time out of mind, there lived in the neighbourhood five saints who had a wide reputation for sanctity, and were objects of ill-will to a wicked magician who dwelt in caverns near. He had in vain tried to bring them into his power, until one day they happened to be crossing the Ogofau, and he, by his wicked enchantments, raised a terrific storm of thunder, lightning and hail, which beat upon and bruised the saints, and they laid their heads against a large boulder standing near for shelter. So great was the force of the hail that the impression of their heads can be seen to this day upon the four sides of the stone.
The enchanter transported the saints into his caverns (the Ogofau) where they sleep. Tradition says they will awake, and come back to the light of day, when King Arthur returns, or when the Diocese is blessed with a truly pious and apostolic prelate!
According to another version they were five young pilgrims on their way to the shrine of S. David, who, exhausted with fatique, reposed on this pillow their weary heads which a violent storm of rain and hailstones affixed to the stone. A malignant sorcerer appeared and carried them off to his cavern, where they are destined to remain asleep until the happy day mentioned.
The block, supposed to have on it the impression of the five heads on each of its four sides, has been extracted from the mine, and was originally horizontal. The hollows are actually mortars in which the quartz was crushed for gold.
This excerpt is from p226 from 'The Lives of the British Saints' by Sabine Baring-Gould (I think he got these stories from Arch Camb 1878 pp322-3).
So maybe it's not even a legit subject for TMA. But it's got some familiar themes that are attached to older stones. And it even seems to have its own new explanation (can the 'gold mortar' thing really be true?)
This stone is thought to be either a Bronze Age standing stone or an anvil stone from a later period (Roman or Medieval). It could conceivably be a standing stone that was later used as an anvil stone.
The stone stands next to the Pumpsaint Gold Mines, which were originally mined by the Romans (or so most people believe). Chris Barber alludes to the stone in his book Mysterious Wales:
Near the entrance to the area containing the Roman gold mines is a strange stone in which the five saints [Ceitho, Celynnen, Gwyn, Gwynog and Gwynaro] are alleged to have left their footprints.
There are other legends relating to these five saints and their activities in the area. There are five pools in the river, which were used by these saints, and later became places of pilgrimage. I'm not sure whether the pools are in Afon Cothi or Twrch, as they both converge at Pumpsaint (another possible indication of prehistoric sanctity).
Of course the village's name means Five Saints in Welsh.
This site is not widely recognised as prehistoric. The National Monument Record states that it is, "possibly Roman, although a medieval, or post-medieval dating would be more conventional".