The present day castle with its adjoining buildings was originally a fortress. There was a stately home with a residential building and a curtain wall already in the 12th century. This is confirmed by archaeological research, which took place during the big reconstruction in 2013.It can be presumed that the Dukes of Zähringen did not take over the compound quite peacefully. Berchtold V had the up to the present day well-preserved monumental donjon integrated in the compound. The Zähriger never intended to live here as they had a residence built in Burgdorf. Yet, it is with this imposing tower that they could leave a sign of their power over the region and the local trading paths. The donjon is unsuitable as a permanent residence as it is actually a single 14-metre high room, which is now called the Grand Hall. In its time an imposing place of representation, today one of the best-preserved representation halls of the Middle Ages.