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 Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.