Montebourg Abbey was probably established by William the Conqueror after the invasion to England (1066). The exact date is unknown, but it was before William's death in 1087. The abbey got lot of donations from the Dukes of Normandy and Kings of England until the 1180s. It had a large land property even in the southern England and the abbey grew up quickly in the 12th century.
The abbey suffered damages in the Hundred Years' War, but it was renovated in the mid-15th century. In 1562 Huguenots looted the abbey during the Frencg Wars of Religion. The first school in Montebourg was established in 1585 and in the 18th century it was used as Catholic poor house and rest home. But soon after the Great Revolution caused the decline of Montebourg Abbey. It was reduced to the state and monastic buildings were partially demolished. In 1842, the Vicar General of Coutances acquired what was by then only an enclosure of ruins, and set it up for the Brothers of Mercy, which he had just formed in order to promote Catholic education in the countryside. From there, the brothers have continued their work.
References:The Gravensteen is a castle in Ghent originating from the Middle Ages. The name means 'castle of the counts' in Dutch. Arnulf I (918–965), Count of Flanders, was the first to fortify this place, building a medieval bastion on this high sand dune, naturally protected by the river Leie and its marshy banks. This bastion consisted of a central wooden building and several surrounding buildings, also in wood.
In the early 11th century, the wooden building was replaced by a stone residence, consisting of three large halls that made up three storeys, connected by a stone stairwell. The monumental stone staircase, the light openings, the fireplaces built into the walls and the latrines were signs of considerable luxury and comfort in those days. There was probably also a tower.