Mont Saint-Michel and fields

The story goes that in 708 CE, the Archangel Michael appeared to Bishop Aubert of Avranches and told him to build a church here and dedicate it to him. Previously, the islet was called “Mont Tombe” (Latin: “Tumba”) but it’s not clear if that’s a reference to existing tombs, or the other meaning of the word: butte or hill. So it was called “Mount Hill”? Ehh, it wouldn’t be the first!