Scheduled ancient monuments
Nationally important sites of an archaeological character and monuments are given legal protection by being placed on a schedule. Only man-made structures, features and remains can be scheduled.
Potential sites are identified by Historic England who advise the Secretary of State on which sites should be added to the schedule. The term 'monument' cover a whole range of archaeological sites, so they may not always be ancient or visible above ground. There are over 200 classes of monuments ranging from prehistoric sites to WWII defences.
Plymouth has 34 scheduled ancient monuments. You can search the full list of locations on the Historic England website.