To what extent the Mohuns were content with the earlier defences of the castle is unknown, but it is remarkable that no mouldings or fragments of Norman ornament have been dug up in or about the building, although there is original Norman work in the parish church. From the configuration of the ground the lines of the old fortress must have been where they still are, so that there would be no reason for pulling down the earlier works to enlarge the area; and yet it is difficult to suppose that works as durable as was the case with those of the Norman period could have fallen to decay by the reigns of Henry III. or Edward I., the date of the oldest extant parts. However this may be, it is certain that the castle of the Mohuns was one of the most important of the western fortresses; and in the lawless days of Stephen it was held for the empress against the king, during the great revolt of 1138, its lord being then William de Mohun, the second baron. William, indeed, was not content with passive resistance. He is described as the “Scourge of the West,” ravaging and plundering the country up to the gates of Barnstaple, where he was held in check by Henry de Tracy. He is said to have been created earl either of Dorset or Somerset, or both, by the empress in 1140; but this creation rests on very uncertain authority, and has never been admitted as valid. The earldoms of that period were very irregular, and some were afterwards set aside. This lord founded the Augustine Priory of Brewton, in Somerset, and, according to the Black Book of the Exchequer, he held forty-four knights’ fees. It is not improbable that to him is due the circular or polygonal keep, which was common at that time where a castle possessed a mound, and which is known to have stood on the summit of the tor.