Grestain Abbey (Abbaye Notre-Dame de Grestain) was an 11th century Benedictine monastery. Closely associated with the family of William, Duke of Normandy, the abbey was instrumental in the Normans taking control over the Catholic Church in England in the centuries following the Norman Conquest of England, establishing new churches and priories in England, and Abbots of Grestain ordained many English priests. Many churches mentioned in the Domesday Book cite Grestain as the founding establishment.
The Abbey was founded in 1050 by Herluin de Conteville and his wife Arlette, mother of William the Conqueror. Herluin, a victim of leprosy, was said to have seen a vision of the Blessed Virgin Mary who told him to take a spa treatment at the source of the Carbec stream in Grestain (Carbec meaning 'the Stream of Kari'). Cured, he decided to build an abbey in the nearby Valley of Vilaine dedicated to the Virgin and a chapel at Carbec, a site also dedicated to the healing spring of Saint-Méen. Herluin's son, Robert de Mortain, half-brother of William, was the principal benefactor, endowing it with his revenues from England.
In 1358, the abbey was sacked by the Anglo-Navarrais. The monks took refuge at their safe house in Rouen, in the parish of Saint-Eloi. Between 1364-1365 the abbey was attacked once more. On the return of the monks, the abbey had been partly destroyed and nearly rased to the ground.
The abbey was officially closed in 1757 on the orders of the bishop. The church buildings were demolished around 1766 and the rest of abbey destroyed in 1790; of these buildings, only a few ruins remain, integrated into the Château de La Pommeraye (a private property): a defensive wall, a 13th-Century portal, an 18th century manor with a 13th century floor, and remains of the church.A monunment has been erected to the memory of the founders who were buried in the now defunct church: Arlette, Herluin and Robert de Mortain, as well as Robert's wife, Mathilde de Montgomerie, daughter of Roger de Montgomerie.References:
The Petersberg Citadel is one of the largest extant early-modern citadels in Europe and covers the whole north-western part of the Erfurt city centre. It was built after 1665 on Petersberg hill and was in military use until 1963. It dates from a time when Erfurt was ruled by the Electors of Mainz and is a unique example of the European style of fortress construction. Beneath the citadel is an underground maze of passageways that can be visited on guided tours organised by Erfurt Tourist Office.
The citadel was originally built on the site of a medieval Benedictine Monastery and the earliest parts of the complex date from the 12th century. Erfurt has also been ruled by Sweden, Prussia, Napoleon, the German Empire, the Nazis, and post-World War II Soviet occupying forces, and it was part of the German Democratic Republic (East Germany). All of these regimes used Petersberg Citadel and had an influence on its development. The baroque fortress was in military use until 1963. Since German reunification in 1990, the citadel has undergone significant restoration and it is now open to the public as a historic site.