Rheineck Castle was probably built in the 12th century. The sources name the count palatine Otto I of Salm as the founder. After his death, King Konrad III seized his estate and transferred it to his brother-in-law, Count Herman of Stahleck. This endeavour resulted in a bitter fight for the County Palatine of the Rhine - a conflict that culminated in the complete destruction of Rheineck Castle by the troops of the King in 1151. Rheineck Castle was rebuilt by the Archbishopric of Cologne by 1164 at the latest but did not, however, withstand the Palatine War of Succession in the 17th century. The Prussian politician von Bethmann-Hollweg inherited the ruin in 1832 and had the main building reconstructed together with the castle chapel. The latter represents a special feature, with its eight-sided design, which is reminiscent of the Carolingian Octagon of Aachen Cathedral. Today, the Castle is in private ownership and cannot be visited.
References:Château de Niort is a medieval castle in the French town of Niort. It consists of two square towers, linked by a 15th-century building and dominates the Sèvre Niortaise valley.
The two donjons are the only remaining part of the castle. The castle was started by Henry II Plantagenet in the 12th century and completed by Richard the Lionheart. It was defended by a rectangular curtain wall and was damaged during the Wars of Religion. In the 18th century, the castle served as a prison.
The present keeps were the central point of a massive fortress. The southern keep is 28m tall, reinforced with turrets. The northern tower is slightly shorter at 23m. Both are flanked with circular turrets at the corners as well as semicircular buttresses. Each of the towers has a spiral staircase serving the upper floors. The Romanesque architecture is of a high quality with the dressed stones closely jointed.