Under the Ancient Monuments and Archaeological Areas Act 1979, as amended by the Historic Environment (Wales) Act 2016, the Welsh Ministers, acting through Cadw, the Welsh Government’s Historic Environment Service, compile and maintain a schedule of monuments of national importance.
A monument may be:
- a building, structure, cave or excavation or the remains thereof;
- a site comprising a vehicle, vessel, aircraft or other movable structure or the remains thereof; or
- any thing or group of things that evidences past human activity.
This permits the scheduling of a wide variety of archaeological and historic sites. Some are completely buried below ground, and are only known through archaeological investigation. Others are far more prominent, and range from prehistoric tombs and hill forts, through the ruins of medieval castles and abbeys, to industrial sites and military remains of the twentieth century. Scheduled monuments often take the form of earthworks or are in in a ruinous or semi-ruinous condition. The criteria for scheduling monuments can be found in Annex A of Technical Advice Note 24: The Historic Environment.