In any historic survey of Derbyshire, however brief, it must not be forgotten that the Normans, for the convenience of civil administration, linked together this county and Nottinghamshire, giving precedence in some respects to the latter. The Assizes, for instance, up to the reign of Henry III., were held only at Nottingham, and the one county gaol for the two shires was in the same town. From the beginning of the reign of Henry III. up to the time of Elizabeth, the Assizes were held alternately at the two county towns. During the whole of this period there was but one sheriff for the two shires; it was not until 1566 that they each possessed a sheriff of their own. Derbyshire possessed a fourth great fortress, which has generally been overlooked; it does not appear on the _Pipe Rolls_, as it was never held by the Crown. Duffield was a convenient centre for the great Derbyshire possessions of Henry de Ferrers. The castle at this place stood on an eminence commanding an important ford of the Derwent, at the entrance of the valley that led to Wirksworth with its lead mines, and hence forwards to the High Peak. Here was erected in early Norman days (as we know from the long-buried remains) a prodigiously strong and massive keep. William, Earl Ferrers, was a stalwart supporter of Henry III. until his death, but his grandson, Robert de Ferrers, soon after he came of age, in 1260, threw himself with ardour into the baronial war against the King. Eventually he was overcome when fighting with his allies at Chesterfield in 1266. Ferrers was taken prisoner, and his life spared; but all his lands, castles, and tenements were confiscated to the crown, and conveyed by Henry to his son Edmund, who was afterwards created Earl of Lancaster. It would be at this period that Duffield Castle was demolished. The foundations of this castle were accidentally discovered in 1886. The lower part of the walls of a great rectangular keep, 95 feet by 93 feet, were brought to light, the walls averaging 16 feet in thickness. These measurements show that Duffield Castle far exceeded in magnitude any other Norman keep, with the single exception of the Tower of London.