A great stone or boulder at Perthiduon measures 3.0m by 23m and up to 1.0m thick, and once lay in a field boundary. Since at least the earlier eighteenth century this has been identified as the capstone of a megalithic tomb, fallen on its supporters. There is a more recent tradition that a number of bronze 'chisels' have been found close to or beneath the stone.

There is no evidence that this is anything other than a large natural boulder, albeit one suitable for use as a capstone.

Sources: Rowlands 'Antiquities ...' (1723), 93
Archaeologia Cambrensis 1 (1846), 467
Wynn Williams in Archaeologia Cambrensis 3rd series 15 (1869), 264
RCAHM Anglesey Inventory (1937), 103
Lynch 'Prehistoric Anglesey' (1970), 51

John Wiles 03.09.07