Ancient monument Wikipedia
In British law, an ancient monument is an early historical structure or monument (e.g. an archaeological site) worthy of preservation and study due to archaeological or heritage interest. The term differs from the American term "National Monument" in that U.S. National Monuments are comparatively few in number and may include natural formations; British Ancient Monuments are by definition man-made.
Ancient monuments are defined by the Ancient Monuments and Archaeological Areas Act 1979 as(a) any scheduled monument (of which there are currently more than 20,000); and
(b) any other monument which in the opinion of the Secretary of State is of public interest by reason of the historic, architectural, traditional, artistic or archaeological interest attaching to it.