I was comparing http://www.geh.org/ar/strip27/htmlsrc/m197927210001_ful.html with http://www.theoldfashionedantiquarian.co.uk/media/DyffrynArdudwy.jpg taken on a visit last September.
A mystery indeed. When was the excavation done FourWinds?
That shows it very well.
The excavation report is dated 1973 and was published in <i>Archaeologia 104</i>