Premise: Builth Castle (Welsh: "Castell Llanfair-ym-Muallt" ) was a castle built under King Edward I, just outside Builth Wells, Powys, Wales. At one time it was an impressive stone-built castle but all the masonry has been removed over the years and all that remains are the mound on which it stood, the ditches and embankments.
Hypothesis: The castle stood on a mound