Granville in the Manche department is perched on Pointe du Roc, surrounded from north to south and west by the English Channel. This spur, made up of Brioverian sandstones and conglomerates present throughout the Massif Armoricain, was formed around 600 million years ago. The ramparts of the old town rise on cliffs 98 to 131 ft (30 to 40 m) high. They are beset by occasional landslides caused by shoreline erosion and waves. Rock reinforcements have been implemented as a reaction, and the north coast is closely monitored.