Castell Mawr, a site just to the south of Castell Henllys in Pembrokeshire, has been considered an Iron Age hillfort for many years. However, in 1988 Harold Mytum and Chris Webster, archaeologists from the Universities of York and Southampton, published a report of their geophysical survey of the site. They concluded that Castell Mawr could be reinterpreted as a Late Neolithic/Early Bronze Age henge, which was later re-used in the Iron Age as an enclosed farmstead. The site is surrounded by Iron Age hill forts (Castell Henllys is only 1200m to the north) and is not particularly defensible. It has no external ditch, but a massive internal one between 10 and 15m wide and still up to 3m deep in places.

I wonder how many other sites have been misinterpreted over the years.