According to Chris Barber in his ‘Mysterious Wales’ the hill the cairn sits on is also known as ‘Bryn-y-Saethau’ – or the Hill of the Arrows, maybe from the stone arrowheads that have been found on its slopes.
The cairn itself is rumoured to be the grave of Boudicca (surely a bit out of the way for a girl from Essex?) or perhaps the resting place of a Roman general. Barber relates a referenceless anecdote (as he likes to do) about a local man walking past in 1938 who saw a field full of Roman soldiers and on the Gop the ghost of a Roman general on a white horse, brandishing a sword. Then ‘a cloud passed over the moon and the apparition vanished’. Personally I think I might have done the vanishing first if it had happened to me. Why do ghosts appear at night I wonder. And was this man on his way home from a local hostelry. We can only speculate.