
You’d think this must be the right stone, but it looks much more grand in this drawing than in the photo (the top seems to match though). William Copeland Borlase says it stands 11 feet 6 inches and nearly 20 feet round, but was only 6 inches into the ground (rather frightening).
archive.org/stream/naeniacornubiaed00borluoft#page/277/mode/1up
From Naenia Cornubiae.