In the article Silbury Hill: A Last Look Inside that I linked to earlier, it says;-

'There are plans to venture beyond previous discussions of Silbury and consider the later uses of the hill. Atkinson reported finding pottery from the Late Saxon/Norman period on the hilltop, and the present excavation found further evidence of this activity. One of the most exciting new theories to have emerged from the project is that the hill’s iconic shape may be the result of significant modification by the placement of a large Saxon or Norman military structure on top; archaeologists believe it may have originally been domed, rather than flat-top as we see today. If so, where was the top of the hill dumped, and what could possibly be found in that material?'

Could it be Weedon/Silbaby?