Le Mont-Saint-Michel is a rocky tidal island and a commune. It was used in the sixth and seventh centuries as an Armorican stronghold of Romano-Breton culture and power, until it was ransacked by the Franks. Before the construction of the first monastic establishment in the 8th century, the island was called "monte tombe". According to legend, St. Michael the Archangel appeared to St. Aubert, bishop of Avranches, in 708 and instructed him to build a church on the rocky islet. During the Hundred Years' War the English made repeated assaults on the island but were unable to seize it, partly because of the abbey's improved fortifications. The Mont-Saint-Michel and its bay were added to the UNESCO list of World Heritage Sites in 1979, as it was listed with criteria such as cultural, historical, and architectural significance, as well as human-created and natural beauty.