The fortress was raised by Onfroi Le Dane in 950, pur up on a Gallo-Roman oppidum ("castle"). When William the Conqueror died, Avranches became his son Henri's privilege. Then Guy de Thouars besieged the city in 1203 and demolished the castle. Guy de Thouars conquered all the Normandy at that time: Rouen, Château-Gaillard, the Mont Saint-Michel...
But in 1229, the English besieged Avranches. The fortress had been ruined, so it must be rebuilt! Too late... Renaud de Gobehen, who led the English, burnt the city in 1346. Avranches was then given to king Charles of Navarre, nicknamed le Mauvais ("the Nasty"). France and England still fought for the stronghold. All those episodes caused the ruin of our keep, which collapsed in the 19th century.