The hill I mentioned next to Stantonbury fort is Winsbury Hill. You can see terracing on the north west side clearly in this google map:

http://maps.google.co.uk/maps?f=q&source=s_q&hl=en&geocode=&q=marksbury&sll=53.800651,-4.064941&sspn=12.478806,28.256836&ie=UTF8&hq=&hnear=Marksbury,+Avon,+United+Kingdom&ll=51.365906,-2.474477&spn=0.003215,0.006899&t=h&z=17