Aulne Abbey was a Cistercian monastery, founded by Saint Landelinus about 637. Before 974 the Benedictines were replaced by secular clerics leading a common life, who, however, embraced the Rule of St. Augustine in 1144.
At the instance of Henry de Leyen, Bishop of Liège, it came into the hands of Cistercian monks from Clairvaux in 1147, under Franco de Morvaux as its first Cistercian abbot. From that time onwards it flourished as a Cistercian monastery.
The French burned it at the end of the 18th century, only a short time after it had been rebuilt on a larger scale. The library, which contained 40,000 books and 5,000 manuscripts, was also destroyed.
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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.