Knap Hill lies on the northern rim of the Vale of Pewsey, in northern Wiltshire, England, about a mile north of the village of Alton Priors. At the top of the hill is a causewayed enclosure, a form of Neolithic earthwork that was constructed in England from about 3700 BC onwards, characterized by the full or partial enclosure of an area with ditches that are interrupted by gaps, or causeways. Their purpose is not known: they may have been settlements, or meeting places, or ritual sites of some kind. The site has been scheduled as an ancient monument.

The Vale of Pewsey or Pewsey Vale is an area of Wiltshire, England to the east of Devizes and south of Marlborough, centred on the village of Pewsey.