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:Saint-Georges de Boscherville Abbey is a former Benedictine abbey. It was founded in about 1113 by Guillaume de Tancarville on the site of an earlier establishment of secular canons and settled by monks from the Abbey of Saint-Evroul. The abbey church made of Caumont stone was erected from 1113 to 1140. The Norman builders aimed to have very well-lit naves and they did this by means of tall, large windows, initially made possible by a wooden ceiling, which prevented uplift, although this was replaced by a Gothic vault in the 13th century. The chapter room was built after the abbey church and dates from the last quarter of the 12th century.
The arrival of the Maurist monks in 1659, after the disasters of the Wars of Religion, helped to get the abbey back on a firmer spiritual, architectural and economic footing. They erected a large monastic building one wing of which fitted tightly around the chapter house (which was otherwise left as it was).