Ramparts of Mont Saint-Michel, Medieval fortification system in Le Mont-Saint-Michel, France

The Ramparts of Mont Saint-Michel are a granite wall partly encircling the island's south and east sides, with round and horseshoe towers and a projecting bastion. The wall's oldest visible sections date from the 13th century, while the walkway and crenellated parapets were added in the 15th century. The wall incorporates gates such as the Porte du Roy and the Porte de l'Avancée, and towers including the Tour du Roy, Tour de l'Arcade, Tour Cholet, and Tour Boucle.

A wooden palisade protected the rock until the early 13th century; after Guy de Thouars' Breton troops ravaged the island around 1204, the abbot and monks began walling it. Abbot Guillaume du Château built the first town wall in 1311, and Robert Jollivet enclosed the lower town in 1417 with a crenellated wall and six towers. Louis XI funded three more towers around 1480, including the Tour Boucle.

The walls enclosed a tight community of traders, craftspeople, and pilgrims whose daily routines revolved around the tides and the rhythm of abbey life. People lived and worked in close quarters, sharing the same narrow passages and gathering spaces for markets and trade.

At low tide you can walk around the outside of the walls, from the Tour Gabriel to the Tour Nord at the base of the rock. The walkway and parapets date from the 15th century, and the route passes the Porte du Roy and its 1430 barbican. Sturdy shoes help on the stone surfaces.

During a conflict spanning several decades in medieval times, a small garrison of about 100 to 150 fighters defended the walls against repeated assaults from vastly larger forces. The island remained under French control throughout and was never captured, despite being surrounded by enemy troops for extended periods.