I think that there's speculation that it was used as some kind of military boundary during the Anglo-Saxon invasion period. Someone, I can't remember the name, wrote a good deal about it in "Arthur:a military history". I didn't know that there was any kind of limitation about how old sites can be on TMA? I think it's perfectly OK to share interests about places from a variety of periods. I've just been reading Blake & Lloyd's stuff about Offa's dyke, which they say is actually an ancient Roman "wall" of Septimus Severus, taking it back into the kind of time-frame you are in.