By the time of the Domesday Book in 1086, Ewyas or Ewias was an autonomous area bounded by the Black Mountains in the west, Graig Syfyrddin in the south, the line of the Golden Valley in the east, and Yager Hill and Cefn Hill to the north, just below the village of Clifford Castle near Hay-on-Wye.
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At around the same time, a religious centre may have been founded at Llanthony, on the site of the later Priory.
Mentioned in Doomsday as a manor belonging to Alfred of Marlborough Baron of Ewyas and a Tenant-in-Chief to King William I. Near Royal Wootton Bassett, the parish of Lydiard Tregoze was part of the Kingsbridge Hundred, while its village originally centred on the medieval parish church of St Mary and the nearby manor house, Lydiard House, which was the home of the St John family, Viscounts Bolingbroke.