Gengenbach Abbey was an Imperial Benedictine Abbey from the late Carolingian period to 1803. It was founded by Saint Pirmin (d. 735) sometime after his expulsion from Reichenau in 727 and settled by monks from Gorze Abbey. It enjoyed good relations with the Carolingian dynasty and soon became an Imperial abbey, with territorial independence. In 1007, however, Emperor Henry II presented it to his newly founded Prince-Bishopric of Bamberg.
Gengenbach was deeply embroiled in the Investiture Controversy and two of its abbots were driven out for supporting the Imperial rather than the Papal cause. Shortly after this, the abbey was involved by Abbot Theoger (1080–1139) of St. George's Abbey in the Black Forest and Bishop Otto of Bamberg in the Hirsauer Reform, during which the abbey church was demolished and rebuilt to the Hirsau model. Subsequently, it has been remodelled in the Gothic, Baroque and neo-Romanesque styles.
During the 13th and 14th centuries, the abbey was instrumental in developing the town of Gengenbach to economic maturity. The abbey avoided further monastic reforms, and although in danger of suppression during the Reformation, survived that too.
In 1575 and 1580, the abbey applied for membership of the Imperial College of Prelates but was refused, due to concern about its Imperial immediacy and Vogtei; membership was eventually approved in 1645 but this approval was not implemented until 1751. The abbey was mediatized in the wake of the German Mediatisation of 1803, and shortly afterwards its territories were absorbed into the state of Baden. However, the abbey was left to function under the last abbot until 1807 when the Grand Duke ordered it secularized.
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.