Wiltshire and Swindon Historic Environment Record http://www.wiltshire.gov.uk/artsheritageandlibraries/museumhistoryheritage/wiltshireandswindonhistoricenvironmentrecord/wshermap.htm?a=d&id=6043 says this is 'a possible bowl barrow or natural mound up to 5m high probably used by the army'. It is certainly an impressive feature on the horizon when seen from the north-east.
Uploaded to Geograph by Vieve Forward on 4 May 2015
Photo © Vieve Forward, 4 May 2015. Licensed for reuse under this Creative Commons licence