If you read Mike Aston -Avon Arch., he puts forward the theory that Solsbury and Bathampton formed the iron age defence of the River Avon on one side of Bath, and that Littledown fort and Stantonbury Fort formed the same role on the otherside, not saying they were defensive all the time. Whatever, it does seem that settlement took place on the higher ground, and Bathampton and Lansdown were where people lived over a long period of time, and Bath itself would have been marshy, probably uninhabitable..
Missing stones; There are loads scattered around the fields up on Lansdown, especially on square enclosure outside Littledown fort (old barrows). Last year at Brockham Wood the farmer pulled two 5 foot stones off the field and dumped them into the hedge, one was "female" triangulate shaped and the other a small long one; weird coincidence or what...