Ancient monument

The term ancient monument is a term in British law.
It is an early historical structure or monument. For example. it may be an archaeological site worth preserving and study. The sites (monuments) are of archaeological or heritage interest. 
The term differs from the American term "national monument". The U.S. National Monuments are few in number and may include natural formations. British ancient monuments are by definition manmade.
Ancient monuments are defined by the Ancient Monuments and Archaeological Areas Act 1979 as