Thanks for looking, I think that Caerwent roman fort being underneath Gray Hill is highly significant. It proves my theory that the Romans focussed on the hills/circles. Their straight roads seem to aim for a lot of the old barrows/circles etc.. As for whether you can see it from Lansdown, well.. it is said that you can see 6 counties from the viewpoint(Devon I do not believe) but two welsh ones definitely. Looking at the map, Gray Hill is not much farther than Penhill (on the way to Glastonbury) which is about the same distance.