The first fort in Belle-Île island was built in 1540 by François of Rohan. It was heavily reconstructed as a large fortress in 1683-1689 according the design of famous fortress architect Sébastien Le Prestre de Vauban. In 1761-63 it was besieged and occupied by the English fleet. Since 1960 it has been a Museum hotel.
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.