Covenant Location

I'm considering an old Cult of Mercury site located in the mountains near the modern Welsh-English border.

What sort of buildings would I expect in an old Roman site in that area (if any) and what sort of problems were in that area in 1220?

Ideally an area of relative wilderness (faerie emphasis.)

EDIT: Oh yes, further information: The magic aura was, up until recently, gone. Since it has returned, it is now being reclaimed.

I remember out Land's End way some iron-age hillforts that had temples built on top of them (after they were taken). Very high hills, very good views, very flat on top, terraced, with steep sides and then the burms and trenches around them.

Just a foundation of granite or marble now. Possibility of low walls if 800 years ago, but it would have had to have been "lost" for no one else to have scavenged the stone as building material.

Roman Temples usually weren't hidden away, but were prominent- a hill, a roadside, etc. A forest etc might have hidden it, but the location would not be featureless topographically.