Do you mean Stukeley's classic serpent drawing Jim? A circular feature is shown on that (search Google Images for Stukeley).

Regarding whether it's much regarded, it seems to be just outside the line of the World Heritage Site so wasn't thought much of at that time...
http://www.eng-h.gov.uk/archcom/projects/summarys/html98_9/images/avebplan.jpg

(The palisade enclosure wasn't included either.)

Time for a rethink?