There's another 'burnt mound' in Birmingham, straddling the tributary that runs through Moseley Bog. Lots of rolled/ firecrazed stones still on show there.
I'm guessing the stones are mostly round as they are 'river rolled' or post glacial. Most mounds i know of were build next to rivers or tributary's.
See, haven't meantioned the R word at all!

Coulpa links to info..

http://www.b13.net/lc_cms/page_view.asp?ID=505

http://www.birmingham.gov.uk/GenerateContent?CONTENT_ITEM_ID=17276&CONTENT_ITEM_TYPE=0&MENU_ID=11889

Give it a visit if your in the area, it's a lovely wildlife reserve, green woodpeckers are just one of the many species living there.