Maen Ceti, generally known as Arthur's Stone, Is a double-chambered megalithic tomb standing in the remnants of a round cairn at 150m above O.D., on the brow of the moderate northern slope of Cefn Bryn, well below the highest part of the ridge.

The names both refer to the massive boulder which serves as a capstone. The Welsh name is first mentioned in a triad of the 16th century, where the raising of the stone is listed as one of the `three mighty achievements of the isle of Britain?. The English name, mentioned in 1695 by Lhuyd as being used `by the common people?, does not seem to have a Welsh equivalent, but s probably of equal antiquity, and originates in the recurrent legend of a pebble from a giant's shoe, in this instance flung in irritation by Arthur from Llanelli.

The cairn does not appear as a mound, but rather as a slight stony bank surrounding a hollow, often water-filled, within which the tomb stands. The bank barely rises above the level of the ground outside, its outer limit being defined as a fairly true circle of 23m diameter where stones begin to protrude from turf to turf, while the inner limit of added material is about 4m towards the centre the stones of the bank vary in size up to 30cm across and are probable derived from excavation of the hollow, in which stones up to 50cm across are included in the irregular surface at 0.8m below ground level.

The hollow plainly results from the construction of the tomb at its centre by underpinning a natural boulder which rested at ground level. The full depth of the original hollow is not visible, so that it remains uncertain whether it was dug in a natural scree deposit or in a regular soil profile overlaying rock. It seems unlikely that the capstone was ever covered by a cairn material, though the stones now distributed in the hollow may have been heaped against the sides.

The upper surfaces of the capstone are rounded by weathering, but the underside is mainly flat and horizontal. Its material is the local conglomerate, containing much quartz, which was also used for the supports and for the stones of the cairn. About one quarter of its mass, consisting of a regular slab 0.5m thick, has fallen to the W., where it lies in one large and two smaller portions. The whole stone originally measured some 4m long by 4m wide by 2.2m high, its weight having been variously measured at 30 and 35 tons. The fallen portion probably became detached through frost action in a natural crack, assisted by the upward thrust of the S.W. supporters. The remainder of the capstone settled at that time to the S.W., pivoting on its three central supports, perching its S. end precariously on a lower point of the most southerly stone, and lifting from the supports at the N. and W.

Two separate chambers have been formed beneath the capstone by the insertion of uprights, of which nine remain in position. The central row of three, which serve as the main weight bearers, have a gap widening enough at the top to allow access between the chambers. Alternatively access to the north chamber would have been possible at its S.E. corner, but the two stones which have fallen outwards at the W., presumably displaced by the falling part of the capstone, would have closed the present access to both chambers on that side. The gap 1.2m wide at the S. end could have been closed by the block now displaced to the S., possibly leaving a smaller gap at the S.E. Both chambers would thus have measured about 1.4m by 1.2m, with similar access; their height above the present infilling of stones does not exceed 0.8m, the true floor being nowhere visible.

On the setting see pp.27-7 above and C. Fox in Arch. Camb., XCII (1937), pp. 159-61.
Published in The Myvyrian Archaiology of Wales (2nd ed., Denbigh, 1870), p.408, No.88.
Additional material supplied by Lhuyd for Camden, Britannia (ed. Gibson), col. 620.
For full account of the names, legends and superstitious practices connected with this monument see Fisher in Arch. Camb., 1920, pp. 331-3. The legend that capstone was split by a blow from St. David's sword `In proof that it was not sacred; and he commanded a well to spring from under it? is possibly no greater antiquity than its record by Iolo Morganwg, ca. 1800. See Iolo MSS.(Welsh Manuscripts society, Llandovery, 1848), pp.82, 473.

RCAHMW, 1976. An Inventory of the Ancient Monuments in Glamorgan, Volume 1: Pre-Norman, Part 1, The stone and bronze ages. Cardiff, Her Majesty's Stationary Office, pp.31-2, Fig. 6, plate 3