Twt Hill is an 11th century earthwork motte and bailey fortress, founded by Robert of Rhuddlan. It occupies a natural spur above the River Clwyd, which is traditionally the site of a Welsh royal residence of Gruffydd ap Llywelyn. Over the next two centuries, the timber castle changed hands between the English and the Welsh several times. In 1241-2 when repairs were recorded, the defences at least in part were still of wood and timber-framed buildings occupied the bailey. Observations of mortar on the motte, suggest the presence of masonry structures but the whole fortification is degraded owing to its sandy composition. The predecessor to Rhuddlan Castle, its large ditched motte still commands the river but only traces remain of the scarped northern bailey.