Petit Bé is a tidal island near Saint-Malo, France, close to the larger island of Grand Bé. There is a fort built in the 17th century. It was part of the defense belt designed by Vauban to protect the city of Saint-Malo from British and Dutch fleets. This belt also included the walls of the Saint Malo, Fort National, Fort Harbour, Fort de la Conchée, and the forts of Cézembre and Pointe de la Varde; these last two have been destroyed. The forts were built by the Saint-Malo engineer Siméon Garangeau.
The fort belonged to the French army until 1885. Later, the army turned the fort over to the city of Saint-Malo. It became a Monument historique in 1921, but was neglected until 2000, when the city gave a free rent to a non-profit organization for the renovation and visiting. At low tide the island can be reached on foot from the nearby Bon-Secours beach.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.