Donjon de Châteaumur is a dungeon built in the 12th century. An enclosure, either made of wood or stone, may have enclosed the keep in an almost circular area. What is certain is that, during this time, the keep was designed as an independent fortress, with a door located on the second floor and protected by a drawbridge that fit into the wall and the doorframe. The interior was divided into two by a partition wall for stability, and it had four levels: a basement and three floors with wooden floors. The ground floor stored provisions, the first floor housed the lord's residence (along with the drawbridge), featuring fireplaces and latrines, and the second floor likely had a guard room with access to the battlements. This top floor was accessible from the first floor via a spiral staircase embedded in the southeast buttress.
Perhaps in the 14th century, during the Hundred Years' War, an enclosure was added. Some parts of it are still visible because the houses around the keep's square are built against it, and there remains a fortified gate for carts. Another larger enclosure surely existed; one can see evidence, for example, just above the chapel's calvary. This could have been a wall or a palisade.
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.