Hay Motte and Bailey

Antiquarian sources have revealed the link between Llanthomas Castle Mound with Hay-on-Wye, Llanigon, Llanthomas and Little Ffordd-Fawr (a ford crossing the River Wye). In Tudor times, Theophilus Jones suggested that Llanigo (Llaneygan in Anglo-Saxon, known today as Llanigon) was named after the first British female saint called Eigen. Saint Eigen lived around the end of the 1st century in the settlement called Trefynys (known today as Llanthomas). The pre-conquest nucleated settlement grew around a church, possibly on the site of the existing church of St. Eigon, in Llanigon.

John Lloyd wrote "the tumulus below Llanthomas is said to direct to the ford on the Wye". William Morgan interpreted this to mean that the castle guarded the road leading down to the River Wye. An Ordnance Survey map (published in 1888) shows that the road connects to the River Wye via the nearby ford called Little Ffordd-Fawr. CPAT indicate that Llanthomas is historically significant because it has "a motte from the early days of the Norman Conquest", and in the Tudor era its "ancient mansion" (as Samuel Lewis called it) was owned by a high-status individual.

Saint Eigen and Caractacus (her father) and the Roman conquest of Britain, the Devereux family and the Norman invasion of Wales and more recently the diarist Francis Kilvert. Francis walked along both sections of Llanthomas lane to visit "Daisy" (daughter of William Thomas), who lived in the modernised domicile of the Llanthomas lordship. The proposal of marriage was made within the walled gardens facing Llanthomas Castle Mound. The history associated with the Llanthomas area may be older.