The position and the layout of Stahlberg Castle clearly indicate that it is founded in the 12th century. It is situated on a rocky projection to the northwest of the town. The ring wall, parts of which have been rebuilt, surrounds the whole area and is rectangular in shape with several openings. A prominent circular tower that rises next to the gateway like a keep was added at the start of the 13th century and secures the narrow entrance with its curtain wall and a ditch. This part of the design is based on a similar feature at Stahleck Castle. The original keep can probably be identified in the ruins of an angular tower in the upper part of the castle.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.