According to Nicholas Thomas – A Guide to Prehistoric England, this is a hill-slope fort and boundary ditch. He goes on to say that it is interesting because it is the only example in Wessex of this type. He also says its less defensive more to do with the herding of cattle, similar to ones found in Cornwall, Devon and South Wales. Date approximately 2nd-1st Century bc.
Two main earthworks – outer one, kidney shaped enclosing 12 acres, and an inner one roughly circular, but not concentric with the outer one, 2.1/2 acres.
A series of ditches radiate out from the Rings, could be late B/A but more likely iron age, being a ‘celtic’ field system, apparently the west ditch is probably the track down to the river for watering the cattle presumably...