In the 8th century, the bishop of the nearby hilltop town of Avranches had a vision where the Archangel Michael told him to build a church atop the island just out to sea. Only accessible when the tidal change permits, from the 10th century onwards, with the help of the Dukes of Normandy, followed by French kings, a major Benedictine abbey developed on the Mont-Saint-Michel. Eventually the island became a symbol of France, for even when the English had taken the rest of Normandy, they never conquered this fortified isle. Visitors can enjoy a walk up through the old town to reach the medieval engineering marvel that is the abbey church. With not enough level ground, huge crypts were constructed to create a level base for this medieval skyscraper.