As Elderford hints, perhaps this stone is a bit young. The coflein record doesn’t commit itself to any period but does admit the stone is on the line of an allegedly Roman road. Still, the romans had to put their roads somewhere. Marie Trevelyan calls the stone ‘Maen yr Ast’, contracted to ‘Mannest’ – or ‘The Bitch Stone’, presumably alluding, like a number of other names, to greyhounds (and perhaps Ceridwen taking the form of a greyhound?)
On Coflein its alternative name is the Peterstone; Peterstone Court lies across the road.
(M. Trevelyan, ‘Folk lore and Folk Stories of Wales’, 1909)