The Château des Tours was built in the 14th century. At that time it had three towers: one had a polygonal interior and was the dungeon, and the others were circular flanking an oblong building on the east and west corners of its south face; then, at the same corners on the north face, there are sentry boxes with Corbels. The oldest part is in the south of the present castle and is also a little higher.
North of the original castle there was a courtyard formed by the castle and crenellated walls outside with wide and deep ditches below. These ditches remain but the walls were replaced in the 16th century by rectangular buildings. At the east and west corners of the north facade there are two round towers, less high than the others, but topped like them with machicolations. There is a door between these two towers above which are the Arms of Calvimont carved on a large stone: they have lain since 1793 a few steps in front of the door.
The castle was restored by Viollet-le-Duc in the 19th century.
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.