Cézembre is an island in the Ille-et-Vilaine département of France, near Saint-Malo. The island is uninhabited, with a surface area of approximately 18 hectares (44 acres), a length of 750 meters, and a width of 300 meters.
The island features a fine sand beach facing Saint-Malo on the south, and a steep and rocky coast around the rest of the island.
Cézembre was inhabited by a number of hermits over the centuries, and featured a monastery for a time. Vauban fortified the island at the end of the 17th century, and it was used thereafter as a place of quarantine.
During World War I, the Belgian Army installed a disciplinary company on Cézembre. During World War II, the island's fortifications were strengthened by the Germans and Italians as part of the Atlantic Wall. The Normandy campaign in the summer of 1944 saw the German-Italian garrison heavily bombarded by land artillery, naval artillery, and air strikes, including some of the first uses of napalm bombs. The island surrendered to elements of the U.S. 83rd Infantry Division at the beginning of September, 1944.
As a result of this intense Allied bombardment, Cézembre's landscape is barren, with little vegetation to this day. The island has not yet been completely demined, and for this reason most of the island other than the beach constitutes a zone interdite (prohibited zone).
Cézembre is claimed as territory by the unrecognised micronation of Talossa.