The ruins of Illens castle stand on a rock wall above a loop of the Saane river. The castle stands on the opposite side of the river from the fortified town of Arconciel. The two castles secured both sides of a crossing (either a ford or a bridge) over the river. The castle is first mentioned between 1150 and 1276.
In 1366, the notoriously violent Count Peter of Aarberg moved into the castle and remained there for a short while. The chamberlain of Charles the Bold, Guillaume de la Baume, expanded the castle and when he left in 1470, it was an elegant and comfortable palace. During the conflicts leading up to the Burgundian Wars, Fribourg and Bernese troops stormed and damaged the building on 3 January 1475.
In 1900, it was partly repaired and expanded and served a community of Trappist monks.
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.