Structure subject to special planning controls. (Protected under the Ancient Monuments and Archaeological Areas Act 1979 in UK.) 

Building place or structure designated as of national importance and protected in the UK under Ancient Monuments and Archaeological Areas Act 1979. See Historic Scotland Memorandum of Guidance 1998. Currently there are some 19,500 entries in the lists covering Schedule Monuments with approximately 35,000 sites ranging from standing stones to teleph [..]

an old or ancient building or other structure, or a site of historical interest that is usually looked after by an official organisation.