the mount became strategically important again in 933 when william "long sword" (the duke of normandy) annexed the cotentin peninsula from the weakened dukes of brittany. this made the mount part of normandy officially. this is shown in the bayeux tapestry, which commemorates (helps remember) the norman conquest of england in 1066. the tapestry shows harold, earl of wessex helping two norman knights from the quicksand around mont-saint-michel during a battle with conan ii, duke of brittany. norman dukes paid for the development of the abbey in the following centuries. it became a good example of norman architecture.