During Henry's minority and the regency of his mother Agnes of Poitou, the Saxon nobles had strengthened their position. The local count Otto of Nordheim, Duke of Bavaria since 1061, had even been involved in Henry's abduction during the 1062 Coup of Kaiserswerth. In turn, the Große Harzburg (Hartesburg) was erected during a large-scale castle building programme in the Duchy of Saxony from 1065 to 1068. Intended as a demonstration of power in the Saxon mainland, the extended complex was strategically sited by King Henry's architect Bishop Benno II of Osnabrück providing protection for the nearby Goslar imperial palace and the mines of Rammelsberg. Its walls extend right up to the steep face of the conical hilltop. At the time it was built the castle was impregnable.