Built by Vauban between 1667 and 1672, the purpose of Citadel of Arras was to protect the city from the attacks (Spanish troops coming from the Netherlands). It has been nicknamed La belle inutile (the beautiful useless one) by residents as it has never been directly involved in heavy fighting and didn't keep the Germans form occupying the city in either Word War. Since 7 July 2008 it is part of the UNESCO World Heritage Sites Fortifications of Vauban which includes eleven other fortifications. Within the citadel on the side of La Place de Manœuvre a small Baroque-style chapel was built. Outside, Le Mur des Fusillés (the wall of the people executed by a firing squad) pays tribute to the 218 members of the French Resistance shot in the citadel's ditch during World War II.
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.