According to legend, the St. Archangel Michael appeared to bishop Ober in a dream and ordered to build a church here. And that was done: in the 8th century a chapel appeared on the rock. However, the Archangel Michael is unlikely to have anything to do with the transformation of the chapel into a fortress, which we see today. The place was strategically and economically profitable, and the abbots were smart enough to use it. But the main merit, of course, belongs to those architects from the 11-16 centuries who managed to unit the man-made and nature so poetically.
Writers and not only they admired Mont-Saint-Michel, called it the eighth wonder of the world. At number one, it entered the UNESCO list.