The Abbey of St. John was a Benedictine monastery in Laon, France, from 1128 to 1766, which replaced a nunnery founded in 641. The prefecture of the department of Aisne now occupies the site.
In 641 Saint Sadalberga, sister of Saint Leudinus Bodo, disciple of Saint Eustace, second abbot of Luxeuil, and widow of Saint Blandinus, retired to Laon, where she founded a nunnery outside the city walls, south of the town. The dedication was to Our Lady ('Notre-Dame'), the same as that of Laon Cathedral. The community grew rapidly to some 300 nuns. Sadalberga then made it a double monastery. She was herself the first abbess. The second abbess was her daughter, Saint Anstrudis.
The abbey had initially followed an adaptation of the demanding Rule of St. Columbanus but later adopted the Rule of St. Benedict. In 1128 the nuns were replaced by a community of Benedictine monks. At around the same time the dedication changed from Our Lady to Saint John the Baptist.
The abbey was partly destroyed in the wars against the Huguenots, but rebuilt in the 17th century. In 1648 it was taken over by the Maurists. The buildings were renovated from 1742. In 1766 the monastery was suppressed. The college of Laon moved into the premises in 1781.
In 1800 the prefect of the department of Aisne took the complex over and today the entire prefecture stands on the site. The physical remains of the former abbey include some buttresses built into the city wall, parts of a church portal and the 18th-century cloister. It is commemorated in the street name 'Rue du Cloître Saint-Jean'.
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.