What is "landesburg"

A Landesburg or landesherrliche Burg ("sovereign castle", "state castle" or "stately castle") was a castle that a territorial lord, such as a prince-bishop, duke or prince built for the defence or expansion of his sovereign estates. They were thus the central and most important castles of the great princely territories. The Landesburgen were usually the property of the territorial lord, but they sometimes referred to castles that he did not own, but were available to him as a safe house (Offenhaus). The large castles of the 8th to 10th centuries, east of the Rhine and outside the towns were often described as Landesburgen because they performed important functions in the control of the state.