What is recorded here

Harry's Walls is an unfinished 16th century artillery castle beside a prehistoric standing stone at Mount Flagon, St Mary's. Men began cutting stone for guns and never finished, leaving the prehistoric marker still visible through the abandoned military work.

The National Heritage List for England records Harry's Walls unfinished 16th century artillery castle and adjacent prehistoric standing stone at Mount Flagon, St Mary's as a scheduled monument. The saved point comes from the centre supplied by the official record. Listing does not by itself mean that the public may enter the place.

Built in the 16th century, likely during the reign of Henry VIII, Harry's Walls is an unfinished artillery castle constructed as part of a coastal defense system against potential French or Spanish invasion. It is important as a rare surviving example of early artillery fortification in England and is associated with the prehistoric standing stone, highlighting the site's layered historical significance.

The historic-place record does not grant public access. Check current conditions and ownership before entering land or a building.